My graphics card only supports 16 colors. Can I still use Java?
Location: http://www.jguru.com/faq/view.jsp?EID=3826
Created: Dec 31, 1999 Modified: 2000-02-21 09:26:10.158
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

All graphical applications require at least 256 colors. Console-based programs like servlets or the compiler are not limited by this capability.

How do I find out the screen size of the user's machine?
Location: http://www.jguru.com/faq/view.jsp?EID=4141
Created: Jan 5, 2000
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

The AWT Toolkit object provides information about the user's runtime platform. To find out what size in pixels the users's screen is, use the getScreenSize() method.

import java.awt.*;
public class Size {
  public static void main(String args[]) {
    // Get toolkit
    Toolkit toolkit = Toolkit.getDefaultToolkit();

    // Get size
    Dimension dimension = toolkit.getScreenSize();

    // Print size
    System.out.println ("Width: " + dimension.width);
    System.out.println ("Height: " + dimension.height);

    // Force exit
    System.exit(0);
  }
}

How do I find out which mouse button is pressed for a MouseEvent?
Location: http://www.jguru.com/faq/view.jsp?EID=4147
Created: Jan 5, 2000
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

For AWT programs, you need to compare the modifiers of the event to the button masks of the INPUT_EVENT.

Left	InputEvent.BUTTON1_MASK
Middle	InputEvent.BUTTON2_MASK
Right	InputEvent.BUTTON3_MASK

For Swing programs, the SwingUtilities class provides three support methods to do the INPUT_EVENT mask checking for you: isLeftMouseButton(), isRightMouseButton(), and isMiddleMouseButton().

The meaning of left, middle, and right assumes a right-handed mouse.

Also, keep in mind that not all users have three-button mice. While there are keyboard alternatives for the addition buttons, consider the awkwardness for users before adding the functionality.

How do I get all the font names supported by java using jdk1.1.8?
Location: http://www.jguru.com/faq/view.jsp?EID=7938
Created: Jan 23, 2000 Modified: 2000-01-23 13:01:49.88
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11)

There are two "types" of font names you can deal with in Java

• Logical Font Names
• System Font Names

Logical font names are the names Java uses for platform independence. These are names like "Serif" and "Dialog". You can obtain these names by calling

String[] fontNames = 
  Toolkit.getDefaultToolkit().getFontList();

System font names are those specific to the operating system on which you are running. The code API does not provide a means to do this in JDK 1.1.8. However, this support is provided in the Java 2 Platform through class GraphicsEnvironment.

You can use Java Native Interface (JNI) to call platform-specific code to obtain the list for JDK 1.1.8, and there are probably some class libraries that provide this support, though it would be platform-specific.

How do I make text typed in a TextArea appear in uppercase only?
Location: http://www.jguru.com/faq/view.jsp?EID=8843
Created: Jan 25, 2000 Modified: 2001-10-01 07:49:41.409
Author: Tim Rohaly (http://www.jguru.com/guru/viewbio.jsp?EID=10) Question originally posed by lyndon mendoza (http://www.jguru.com/guru/viewbio.jsp?EID=8369

The key to solving this problem is to subclass TextArea and intercept any KeyEvent sent. You need to check to see if the typed key is a lower case character (be careful to keep this independent of Locale!) - if it is, change it to upper case.

Here's a piece of code that will do this for you:

import java.awt.AWTEvent;
import java.awt.TextArea;
import java.awt.event.KeyEvent;

public class UpperCaseTextArea extends TextArea {

    public UpperCaseTextArea() {
        enableEvents(AWTEvent.KEY_EVENT_MASK);
    }

    public void processKeyEvent(KeyEvent e) {
        if ((e.getID() == KeyEvent.KEY_TYPED) &&
            Character.isLowerCase(e.getKeyChar()) ) {
            e.setKeyChar(Character.toUpperCase(e.getKeyChar()));
        }
        else {
            super.processKeyEvent(e);
        }
    }
}

And here's a little application you can use to test it:

import java.awt.Frame;
import java.awt.BorderLayout;
import java.awt.event.KeyEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class UCTextAreaTest {

    public static void main(String[] args) {
        Frame f = new Frame();
        f.add(new UpperCaseTextArea(), BorderLayout.CENTER);
        f.addWindowListener(
            new WindowAdapter() {
                public void windowClosing(WindowEvent e) {
                    System.exit(0);
                }
            }
        );
        f.setSize(200, 150);
        f.setVisible(true);
    }
}

Why must I override getPreferredSize() for Canvas to appear on the screen?
Location: http://www.jguru.com/faq/view.jsp?EID=8937
Created: Jan 26, 2000 Modified: 2000-01-26 05:38:18.498
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by arul senthil (http://www.jguru.com/guru/viewbio.jsp?EID=8904

Whenever you use a component in a layout manager, it may be asked for its preferredSize. This is a layout manager's way of respecting the sizing wishes of components that it manages. Some layout managers try to respect it, while others may ignore it.

The preferredSize property is a component's way of saying how big it wants to be to be comfortable. In the case of a Canvas, there is nothing to display, so its preferredSize is (0,0). Because of this, if it is placed in a layout manager that respected preferredSize(), like BorderLayout or FlowLayout, it will take up no space and appear invisible.

You should never "set" the preferredSize of any component from the outside. Swing components allow you to do this, but it is a very bad idea. The preferredSize should always be computed based on what the component displays. A Button, for example, figures out how big the text will be, and adds some room for the border around that text. A Panel asks its layout manager (assuming one has been set) for a preferredSize, so all of its contained components can be taken into account.

You should override the getPreferredSize() method of Canvas to return a size appropriate for what you are displaying. Depending on what is displayed, the preferredSize may need to change. For example, if you're displaying a graph and a new month is added to its x-axis, the preferred width may need to increase. Override getPreferredSize() to return the proper computed preferred size.

What exactly is the "Event Dispatch" thread (aka "AWT" Thread)?
Location: http://www.jguru.com/faq/view.jsp?EID=8963
Created: Jan 26, 2000 Modified: 2000-02-01 06:16:27.889
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by Mohamed M. (http://www.jguru.com/guru/viewbio.jsp?EID=3439

When you run a GUI applet or application, the code in your main() method creates a GUI and sets up event handling. When you call setVisible(true) for your Frame, Window, Dialog, or when the browser displays the Applet, the user must be able to interact with the GUI.

The problem is that your main() method may not end at that point. It could be busy doing some other task, such as computing PI to 40,000 decimal places. If the user had to wait for the main() method to finish before they could interact with the GUI, they could end up quite unhappy.

So the AWT library implements its own thread to watch GUI interaction. This thread is essentially a little loop that checks the system event queue for mouse clicks, key presses and other system-level events. (You can also put your own events in the system queue, but that's another story...).

The AWT thread (aka the "Event Dispatch" thread) grabs a system event off the queue and determines what to do with it. If it looks like a click on top of a component, it calls the mouse click processing handler for that component. That component, in turn, could fire other events. For example, if you click on a JButton, the AWT thread passes the mouse click to the JButton, which interprets it as a "button press", and fires its own actionPerformed event. Anyone listening will have their actionPerformed method called.

The AWT thread also handles repainting of your GUI. Anytime you call repaint(), a "refresh" request is placed in the event queue. Whenever the AWT thread sees a "refresh" request, if examines the GUI for damaged areas or components marked invalid (ie, the text has changed on a Label), then calls the appropriate methods to layout the GUI and paint any components that require painting.

Note: The AWT "thread" may in fact be implemented by multiple threads under some runtime environments. These threads coordinate effort to watch for mouse clicks, keypresses, repaint requests, etc. As far as you're concerned you can treat this all as one "AWT thread".

AWT components are threadsafe, in that if you call a Label's setText() method, it synchronizes such that the displayed text cannot appear with a partially old value and partially new value. However, Swing components, are generally not threadsafe. Because of this, you must make sure that any changes to Swing components that might affect their display are done through the AWT event thread. If the same thread both updates and displays a component, you are guaranteed that the display is consistent.

You can use SwingUtilities.invokeLater() or SwingUtilities.invokeAndWait() to defer processing to the AWT thread.

Can you create custom cursors in JDK 1.1?
Location: http://www.jguru.com/faq/view.jsp?EID=8974
Created: Jan 26, 2000 Modified: 2000-01-26 06:10:18.888
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by Jean-Yves BRUD (http://www.jguru.com/guru/viewbio.jsp?EID=8908

You cannot create custom cursors in JDK 1.1. This support is only available in the Java2 platform.

In JDK 1.1, you can only set cursors to the constant values provided in the java.awt.Cursor class.

How can I change the size of an Applet/JApplet in a Web Page?
Location: http://www.jguru.com/faq/view.jsp?EID=8992
Created: Jan 26, 2000 Modified: 2000-01-26 09:00:20.531
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by Venkata Reddy Vajrala (http://www.jguru.com/guru/viewbio.jsp?EID=3588

Short answer: you can't.

The browser defines a fixed-sized area in the web page for the Applet. If you need dynamic sizing, your only choice is to have your Applet display a Frame, Window, or Dialog (or their Swing equivalents).

Note that just because the Applet doesn't change size, you should not avoid layout managers. Layout managers are still important because the components could appear different sizes based on the user's font settings or locale (if your program localizes).

How are individual pixels represented in memory?
Location: http://www.jguru.com/faq/view.jsp?EID=9765
Created: Jan 28, 2000 Modified: 2000-02-14 08:55:24.887
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

Each pixel is stored as a 32 bit integer (int). The int packs four unsigned bytes within it, one for each of the alpha, red, green, and blue (ARGB) color planes, in that order.

Alpha (8-bits)	Red (8-bits)	Green (8-bits)	Blue (8-bits)
32 bit pixel

To get at each value, you would use a masking operation and a bit shift :

int alpha = (pixel & 0xff000000) >> 24;
int red   = (pixel & 0x00ff0000) >> 16;
int green = (pixel & 0x0000ff00) >> 8;
int blue  = (pixel & 0x000000ff) >> 0;

Keep in mind that you cannot store each value in a byte as bytes are signed.

How do you create custom cursors with the Java 2 platform?
Location: http://www.jguru.com/faq/view.jsp?EID=9958
Created: Jan 29, 2000 Modified: 2000-01-31 08:11:21.708
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

The createCustomCursor() method of the Toolkit class provides for the ability to create a cursor out of an Image.

When creating custom cursors, be sure to take advantage of the hints available from the getBestCursorSize() and getMaximumCursorColors() methods.

How do I create a window that always stays on top of my application?
Location: http://www.jguru.com/faq/view.jsp?EID=9991
Created: Jan 30, 2000 Modified: 2000-01-31 08:14:48.627
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

Without resorting to native code, you cannot do this.

How do we build a TabbedPane component using AWT?
Location: http://www.jguru.com/faq/view.jsp?EID=10323
Created: Jan 31, 2000 Modified: 2000-01-31 08:34:01.989
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by vinay babu (http://www.jguru.com/guru/viewbio.jsp?EID=10197

Swing provides a component called JTabbedPane that is rather good.

If you cannot (or don't want to) use Swing for some reason, there are several ways to do this.

The most common one is to create a custom Panel subclass that uses a CardLayout to display its children, and provide a set of buttons along an edge to switch between components. Other ways are more manual to track the components.

For an example (free with source code, for any use other than simply selling it) please see Scott Stanchfield's TabSplitter at http://www.javadude.com/tools/tabsplitter.

How do you change the coffee cup icon that appears in the top corner of frames?
Location: http://www.jguru.com/faq/view.jsp?EID=10385
Created: Jan 31, 2000 Modified: 2000-07-25 20:36:40.75
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

The setIconImage() method of the Frame class permits you to alter the icon displayed.

Image image = ...;
aFrame.setIconImage(image);

See How do I display an Image in an Applet or Application? for how to load the image.

When do I use adapter classes vs. interfaces in "new" expressions for event handling?
Location: http://www.jguru.com/faq/view.jsp?EID=10618
Created: Feb 1, 2000 Modified: 2000-02-01 06:51:05.129
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by Gopal Saha (http://www.jguru.com/guru/viewbio.jsp?EID=10163

When you register an event handler, you must pass it an instance of some class that implements its listener interface.

Simple Event Handler

Start with a simple example. Suppose we want to print "Hello" when a button is pressed. Button fires an actionPerformed event when pressed, which is the only method in the ActionListener interface. We could write the following code to accomplish this task:

SayHello.java

import java.awt.*;
import java.awt.event.*;

public class SayHello implements ActionListener {
  public void actionPerformed(ActionEvent e) {
    System.out.println("Hello");
  }
}

 

SimpleGUI.java

import java.awt.*;

public class SimpleGUI {
  public static void main(String[] args) {
    Frame f = new Frame();
    Button b = new Button("Press me");
    b.addActionListener(new SayHello());
    f.add(b);
    f.setVisible(true);
    // application exit handler omitted
  }
}

Simple Anonymous Inner Class

It seems like a waste to create an entirely new class just to say "Hello". This uses up a class name in our namespace, and unique names can be difficult to create.

To help this, we create an anonymous inner class by writing the event handler class code in the call to register the event handler. The new test class looks as follows:

SimpleGUI2.java

import java.awt.*;
import java.awt.event.*;

public class SimpleGUI2 {
  public static void main(String[] args) {
    Frame f = new Frame();
    Button b = new Button("Press me");
    b.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        System.out.println("Hello");
      }});
    f.add(b);
    f.setVisible(true);
    // application exit handler omitted
  }
}

ActionListener is an interface! Whenever you see "new" followed by an interface name and a "{" (open curly brace), you're creating an anonymous inner class. You would read

new ActionListener() { ... }

as "Create a new instance of some class (we don't care what its name is) that implements ActionListener, and the details are in the curly braces."

This is a convenient shorthand for creating event handlers.

Event Adapters

Some event listener interfaces require several methods. For example, WindowListener requires seven methods. Normally, you only care about one of these methods, windowClosing. If we were to write an anonymous inner class to close an application, it might look as follows

Frame f = new Frame();
f.addWindowListener(new WindowListener() {
  public void windowClosing(WindowEvent e) {
    System.exit(0);
  }
  public void windowClosed(WindowEvent e) {}
  public void windowOpened(WindowEvent e) {}
  public void windowIconified(WindowEvent e) {}
  public void windowDeiconified(WindowEvent e) {}
  public void windowActivated(WindowEvent e) {}
  public void windowDeactivated(WindowEvent e) {}
});

All of those dummy methods are really a lot of noise. In java.awt.event, Sun defined a class called WindowAdapter that implements WindowListener with seven dummy methods. This means that you can extend WindowAdapter and you only need to override the classes you care about. The above code becomes:

Frame f = new Frame();
f.addWindowListener(new WindowAdapter() {
  public void windowClosing(WindowEvent e) {
    System.exit(0);
}});

You read the anonymous inner class above as "create an instance of some class (we don't care what its name is) that extends WindowAdapter, and the details are in the curly braces."

The full example for the button press and window close follows:

SimpleGUI3.java

import java.awt.*;
import java.awt.event.*;

public class SimpleGUI3 {
  public static void main(String[] args) {
    Frame f = new Frame();
    Button b = new Button("Press me");
    b.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        System.out.println("Hello");
      }});
    f.add(b);
    f.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
        System.exit(0);
    }});
    f.setVisible(true);
    // application exit handler omitted
  }
}

How do I get rid of the Unsigned Java Applet Window message at the bottom of windows/frames I create in my applet?
Location: http://www.jguru.com/faq/view.jsp?EID=11000
Created: Feb 2, 2000 Modified: 2000-09-13 13:37:36.369
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

This is a security feature to prevent untrusted applets from displaying what appear like trusted windows. If you sign your applet and the user trusts you, the message will go away.

What is a peer?
Location: http://www.jguru.com/faq/view.jsp?EID=11353
Created: Feb 4, 2000 Modified: 2000-02-04 06:50:13.207
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by John Zukowski PREMIUM (http://www.jguru.com/guru/viewbio.jsp?EID=7

AWT uses native code (code specific to a single operating system) to display its components. Each implementation of the Jave Runtime Environment (JRE) must provide native implementations of Buttons, Labels, Panels, and all of the other AWT components.

Whenever you use an AWT component, if forwards all of its drawing requests to a piece of native code. This allows you to generically use an AWT Button in your application, but the Button appears as a Windows Button, a Motif Button, a Mac Button, or a real button on whatever platform you are running.

These pieces of native code are referred to as peers, as they share the responsibility for displaying a component.

Peer code includes native code to display components, as well as draw lines, determine platform specifics such as current screen size, and other native platform issues.

Note that the Swing components do use peers for two tasks. First, Swing's JFrame, JWindow, JDialog and JApplet extend their AWT counterparts. They all use peers to display a real drawing area on the screen.

Other Swing components are lightweight; they do not have peers. These components draw themselves on top of an existing JFrame, JWindow, JDialog or JApplet. However note that the drawing functions are implemented using peers, so they actually use peers as well, though not as their complete implementations.

How do I get the native window pointer to an AWT Window?
Location: http://www.jguru.com/faq/view.jsp?EID=11518
Created: Feb 4, 2000 Modified: 2000-02-05 07:38:58.931
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

This capability is currently not supported.

Can I use the Java2D capabilities with the 1.1 Java runtime environment?
Location: http://www.jguru.com/faq/view.jsp?EID=11525
Created: Feb 4, 2000 Modified: 2000-07-01 22:20:36.696
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

The short answer is no. The libraries are part of the standard Java 2 platform release (starting with version 1.2). Since they modify core classes in the java.awt.* libraries, you can not pull them out and use them with another version. They are not a standard extension like Swing, but part of the standard release.

How do I use layout managers to compose a GUI?
Location: http://www.jguru.com/faq/view.jsp?EID=11659
Created: Feb 5, 2000 Modified: 2000-05-29 11:54:18.162
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11)

See Effective Layout Management at the Java Developer Connection.

How can I simulate user interaction (key press, mouse click) on a component?
Location: http://www.jguru.com/faq/view.jsp?EID=11818
Created: Feb 6, 2000 Modified: 2000-02-07 07:33:25.564
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by lyndon mendoza (http://www.jguru.com/guru/viewbio.jsp?EID=8369

The 1.3 Java release includes a Robot class to generate low-level native mouse / keyboard input events at the operating system level.

The other alternative is to call postEvent() of the EventQueue class.

How do I center a dialog on top of a frame?
Location: http://www.jguru.com/faq/view.jsp?EID=12670
Created: Feb 9, 2000 Modified: 2000-02-09 07:56:40.664
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11)

When you create a dialog, you must pass it the parent Frame. This Frame can be obtained via the Dialog's getParent() method. We'll define a subclass of Dialog called CenterableDialog that will look at the parent Frame and determine where to place the dialog. We must be careful and watch out for the screen edges too!

The CenterableDialog class

Here's the code. Once you define this class, all you have to do is:

• Use CenterableDialog wherever you would normally use Dialog
• Call showCentered() instead of show() to display the dialog. The reason we don't override show() itself is so we can still explicitly set the dialog's position and show() it non-centered.

import java.awt.Dialog;
import java.awt.Dimension;
import java.awt.Point;
import java.awt.Frame;

public class CenterableDialog extends Dialog {

  public CenterableDialog(Frame parent) {
    super(parent);
  }
  public CenterableDialog(Frame parent,
                          String title) {
    super(parent, title);
  }
  public CenterableDialog(Frame parent,
                          String title,
                          boolean modal) {
    super(parent, title, modal);
  }
  public CenterableDialog(Frame parent,
                          boolean modal) {
    super(parent, modal);
  }

  public void showCentered() {
    Frame parent = (Frame)getParent();
    Dimension dim = parent.getSize();
    Point     loc = parent.getLocationOnScreen();

    Dimension size = getSize();

    loc.x += (dim.width  - size.width)/2;
    loc.y += (dim.height - size.height)/2;

    if (loc.x < 0) loc.x = 0;
    if (loc.y < 0) loc.y = 0;

    Dimension screen = getToolkit().getScreenSize();

    if (size.width  > screen.width)
      size.width  = screen.width;
    if (size.height > screen.height)
      size.height = screen.height;

    if (loc.x + size.width > screen.width)
      loc.x = screen.width - size.width;

    if (loc.y + size.height > screen.height)
      loc.y = screen.height - size.height;

    setBounds(loc.x, loc.y, size.width, size.height);
    show();
  }
}

What about FileDialog?

You can use the same subclass trick on FileDialog -- it would look exactly the same as the above, except for the name of the class.

When used in an Applet/JApplet, does a Frame/JFrame show up inside the web page or as a new window?
Location: http://www.jguru.com/faq/view.jsp?EID=13602
Created: Feb 12, 2000 Modified: 2000-02-12 07:15:02.056
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by Duane Vigue (http://www.jguru.com/guru/viewbio.jsp?EID=12977

If you add components to an Applet or JApplet, they will appear in the web page's assigned spot for the applet.

If you create a new Frame, Window, or Dialog (or their Swing equivalents), they will always appear as a separate window (complete with a small Warning tag to indicate they were created by an applet -- see the certificate FAQ, http://www.jguru.com/jguru/faq/view.jsp?EID=11475).

If you would like to have Frames appear in the web page itself, you could add a JDesktopPane to a JApplet, and add JInternalFrames to it. This of course requires Swing, and the best way to ensure this is to use the Java Plug-in from Sun (http://java.sun.com/products/plugin/).

How do I convert an in-memory bitmap to something that is usable by JAVA?
Location: http://www.jguru.com/faq/view.jsp?EID=13924
Created: Feb 13, 2000 Modified: 2000-02-14 08:40:18.838
Author: Finlay McWalter (http://www.jguru.com/guru/viewbio.jsp?EID=13911) Question originally posed by Steven Cote (http://www.jguru.com/guru/viewbio.jsp?EID=11054

Jef Poskanzer has a 1.1-compliant GIF writer: http://www.acme.com/java/software/Acme.JPM.Encoders.GifEncoder.html

How can I capture the image of an AWT GUI?
Location: http://www.jguru.com/faq/view.jsp?EID=14471
Created: Feb 15, 2000 Modified: 2000-05-24 05:39:56.497
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by RaghuNath Boyalakuntla (http://www.jguru.com/guru/viewbio.jsp?EID=12873

You can use the printAll() method of Component to accomplish this.

As an example

Component comp = ... ; // the top-level component
                       // you want to capture

// create an image for the capture
Image img  = comp.createImage(comp.getWidth(), comp.getHeight());

// grab a graphics context for that image
Graphics g = img.getGraphics();

// print the GUI into that image
comp.printAll(g);

The resulting Image contains a picture of the GUI. Note that if the GUI is not displayes, you either need to display it first or call addNotify() on it to create the necessary peer components.

Can I use menus and a menu bar in an applet?
Location: http://www.jguru.com/faq/view.jsp?EID=15630
Created: Feb 18, 2000 Modified: 2000-02-18 13:16:57.344
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

AWT applets (those that subclass java.applet.Applet) cannot include an AWT MenuBar. Swing applets (those that subclass javax.swing.JApplet) can use the JMenuBar. To display menus in an AWT you would either need to create an external Frame to place them in or create your own custom components that simulated the behavior of menus on menu bars.

I tried adding the same menu item to multiple menus. Why doesn't it work properly?
Location: http://www.jguru.com/faq/view.jsp?EID=15643
Created: Feb 18, 2000 Modified: 2000-02-18 13:53:05.223
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

When adding a component to a container, it is removed from any previous container. Because of this, you cannot have the same component/menu items in multiple containers/menus.

How can I limit the size of my window?
Location: http://www.jguru.com/faq/view.jsp?EID=15690
Created: Feb 18, 2000 Modified: 2000-02-18 14:12:48.188
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

You can register a ComponentListener with the window and have the componentResized() method validate the window size. If the window is outside acceptable limits, you can return things to the desired size.

How do I force drawImage() to refetch an image?
Location: http://www.jguru.com/faq/view.jsp?EID=15705
Created: Feb 18, 2000 Modified: 2000-02-21 03:42:22.595
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

If you flush() an Image between calls to drawImage(), the Image will be refetched instead of using the local cached version.

What is the difference between JFC & WFC?
Location: http://www.jguru.com/faq/view.jsp?EID=16247
Created: Feb 20, 2000 Modified: 2000-02-21 03:49:59.617
Author: Jeff Mackay (http://www.jguru.com/guru/viewbio.jsp?EID=16238) Question originally posed by Dheeraj Bhatia (http://www.jguru.com/guru/viewbio.jsp?EID=14903

JFC supports robust and portable user interfaces. The Swing classes are robust, compatible with AWT, and provide you with a great deal of control over a user interface. Since source code is available, it is relatively easy to extend the JFC to do exactly what you need it to do. But the number of third-party controls written for Swing is still relatively small.

WFC runs only on the Windows (32-bit) user interface, and uses Microsoft extensions to Java for event handling and ActiveX integration. Because ActiveX components are available to WFC programs, there are theoretically more controls available for WFC than for JFC. In practice, however, most ActiveX vendors do not actively support WFC, so the number of controls available for WFC is probably smaller than for JFC. The WFC programming model is closely aligned with the Windows platform--it doesn't extend (or even interoperate with) AWT, so it feels more like programming with VB than with Java. Source code is not available, so you're on your own when extending the library.

In terms of functionality, WFC and JFC are similar: they both offer a similar range of controls, they both support clipboard and drag-n-drop operations, etc. WFC performance is better than JFC, and in general, memory requirements for WFC are lower than for JFC. For simple user interfaces, WFC is easy to develop with. For more complex user interfaces, WFC is more difficult than JFC. WFC was written with a component mindset: the details of any specific component are hidden within the component. JFC was written with an object-oriented mindset, providing a greater degree of control.

The bottom line is: If you need a robust, cross platform user interface, use JFC. If you're writing a quick and simple front-end, and if all of your clients are running Windows, and if you don't mind the Microsoft-specific extensions to Java, consider using WFC.

How can I display images in an TextArea?
Location: http://www.jguru.com/faq/view.jsp?EID=16251
Created: Feb 20, 2000 Modified: 2000-02-21 03:52:44.06
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Nelson Nazareth (http://www.jguru.com/guru/viewbio.jsp?EID=14700

AWT TextArea components only support displaying text. You cannot display images in them. If you don't mind using the Swing components, you can use either the JEditorPane or JTextPane to display images within text components.

How can I display Text strings of different style on different lines of an TextArea. i.e I want Hello on first line as PLAIN String. Hello World on second line as BOLD. or might be in different Color.
Location: http://www.jguru.com/faq/view.jsp?EID=16252
Created: Feb 20, 2000 Modified: 2000-02-21 03:53:26.393
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Nelson Nazareth (http://www.jguru.com/guru/viewbio.jsp?EID=14700

The AWT TextArea only supports displaying its text in a single color and single font. To display text in different styles, you can use the Swing JTextPane or JEditorPane (or create your own component).

Where can I get information about writing a layout manager?
Location: http://www.jguru.com/faq/view.jsp?EID=16253
Created: Feb 20, 2000 Modified: 2000-02-21 03:54:39.06
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Alexey Lonshakov (http://www.jguru.com/guru/viewbio.jsp?EID=10550

Sun's online tutorial describes what you need to do to create a layout manager at http://java.sun.com/docs/books/tutorial/uiswing/layout/custom.html.

How do I overcome the 32K limit of TextArea?
Location: http://www.jguru.com/faq/view.jsp?EID=16267
Created: Feb 20, 2000 Modified: 2000-02-21 03:40:57.973
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

On Windows 95 machines, the AWT TextArea is limited to about 32K characters. This is a limitation of the underlying operating system. Since AWT components rely on native components, you cannot override this behavior from within Java. If you need larger text areas, you need to either convince your users to not use Windows 95 or use a component other than TextArea, like the Swing JTextArea, that doesn't have this limit.

How do I create multi-line labels in AWT / Swing?
Location: http://www.jguru.com/faq/view.jsp?EID=16550
Created: Feb 21, 2000 Modified: 2000-02-23 08:21:24.588
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

The AWT Label does not support multiple lines on Label. You would need to create multiple Label components and place them in a Panel (or create your own component).

In Swing 1.1.1 and later, you can place HTML in your labels to get a multi-line label, as in

String htmlLabel = "<html><sup>HTML</sup> <sub><em>Label</em></sub><br>" +
      "<font color=\"#FF0080\"><u>Multi-line</u></font>";
JLabel label = new JLabel(htmlLabel);

If you want to be able to use \n and \r to indicate new lines, you would need to define your own UI for the Swing component.

How can I explicitly display a tooltip in AWT?
Location: http://www.jguru.com/faq/view.jsp?EID=17099
Created: Feb 23, 2000 Modified: 2000-12-27 08:55:58.195
Author: Christophe Caissotti (http://www.jguru.com/guru/viewbio.jsp?EID=17093)

Here's some sample code that can display a tooltip in an AWT GUI.

Users can see information each time they move the mouse on a GUI. This little class displays tips given by a String. The String can include five Html tags: <br><b><i></i></b>

You can download the class file at http://www.chez.com/ccaissotti/components/tipProducer.java

To display a tip, just create a TipProducer with the String you want to show and call its draw() method.

For example

public void onMouseMove( MouseEvent me ) {
  tp = new tipProducer();
  tp.setString("Click on the point<br>x=<b>" + me.getX() +
               "</b><br>y=<b>"+me.getY()+
               "</b>" );
  tp.draw(g, me.getX(), me.getY );
}

How can I iconify/deiconify my Frame/JFrame?
Location: http://www.jguru.com/faq/view.jsp?EID=17415
Created: Feb 23, 2000 Modified: 2000-02-25 06:09:05.032
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

The setState() method introduced to Java 1.2 provides support for iconifying and deiconifying.

frame.setState(Frame.ICONIFIED);
frame.setState(Frame.NORMAL);

How do I maximize a Frame/JFrame ?
Location: http://www.jguru.com/faq/view.jsp?EID=17416
Created: Feb 23, 2000 Modified: 2000-02-25 06:11:51.009
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by John Zukowski PREMIUM (http://www.jguru.com/guru/viewbio.jsp?EID=7

There is no direct support for this. The best you can do is make sure the frame is deiconified then set its size to the screen size.

frame.setState(Frame.NORMAL);
Toolkit toolkit = Toolkit.getDefaultToolkit();
Dimension dimension = toolkit.getScreenSize();
frame.setSize(dimension);

[FAQ Manager Note] The operating system will not treat this as a maximized frame, so in general this is not a good idea for simulating maximize. I'd recommend that you only set the state to NORMAL to ensure the window is visible (not minimized/iconified) and allow the user to press the maximize button if they want.

How can I make a TextField accept and display ASCII characters like the smiley?
Location: http://www.jguru.com/faq/view.jsp?EID=17637
Created: Feb 24, 2000 Modified: 2000-02-25 06:15:34.315
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by lyndon mendoza (http://www.jguru.com/guru/viewbio.jsp?EID=8369

Java uses the Unicode character encodings. While 0-127 map directly from Unicode to ASCII, how they display may appear different. For instance, while \u0001 might appear as a smiley face under ASCII, the smiley face isn't in the Unicode code chart. You can use the UnicodeDisplay example from Java Examples in a Nutshell (http://www.oreilly.com/catalog/jenut/examples/UnicodeDisplay.java) to see exactly what characters are available for display.

How do I read an Image from a JAR file with Netscape browsers?
Location: http://www.jguru.com/faq/view.jsp?EID=17781
Created: Feb 24, 2000 Modified: 2000-09-14 07:41:44.11
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

The Communicator 4.x browsers do not implement the Class.getResource(), ClassLoader.getResource(), and ClassLoader.getSystemResource() methods. You need to use the Class.getResourceAsStream(), ClassLoader.getResourceAsStream(), or ClassLoader.getSystemResourceAsStream() methods instead, respectively. See http://developer.netscape.com/docs/technote/java/getresource/getresource.html for more information.

With that said, the following will load an Image:

InputStream in = getClass().getResourceAsStream("image.gif"); 
byte buffer[] = new byte[in.available()]; 
in.read(buffer); 
Image image = Toolkit.getDefaultToolkit().createImage(buffer); 

How do I get FilenameFilter to work on my FileDialog?
Location: http://www.jguru.com/faq/view.jsp?EID=17853
Created: Feb 24, 2000 Modified: 2001-08-20 11:00:38.007
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

Basically, it doesn't work on Windows machines.

The JFileDialog provides a better alternative that supports filters, if you can use the Swing component set.

See Bug 4031440 for more information: http://developer.java.sun.com/developer/bugParade/bugs/4031440.html.

How can I embed small images into the .class file that uses them so that I don't have to download so many separate files?
Location: http://www.jguru.com/faq/view.jsp?EID=19095
Created: Feb 28, 2000 Modified: 2000-03-06 19:32:03.314
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by John Zukowski PREMIUM (http://www.jguru.com/guru/viewbio.jsp?EID=7

Try to follow the strategy followed by the javax.swing.Icon interface. Read all about it at http://java.sun.com/products/jdk/1.2/docs/api/javax/swing/Icon.html

You can use something like this -

private static class MenuArrowIcon implements Icon, UIResource, Serializable {
:
:
:
} // End class MenuArrowIcon

from the

javax/swing/plaf/basic/BasicIconFactory.java

You can initialize an int array and use either

java.awt.image.MemoryImageSource

http://java.sun.com/products/jdk/1.2/docs/api/java/awt/image/MemoryImageSource.html

java.awt.image.BufferedImage

http://java.sun.com/products/jdk/1.2/docs/api/java/awt/image/BufferedImage.html

When I fill a Choice with more than 30000 Strings, why doesn't it show all of them?
Location: http://www.jguru.com/faq/view.jsp?EID=20513
Created: Mar 5, 2000 Modified: 2000-03-06 19:52:22.899
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Mayur Adatia (http://www.jguru.com/guru/viewbio.jsp?EID=14325

The AWT Choice component is limited to the capabilities of the associated native control of the user's platform. Sounds like it has a 32K limit for your platform.

As a user, I would hate the user interface if I was expected to pick something from over 30,000 choices. You might consider designing an interface that limited the number of options to something a little more reasonable.

How do I make sure an Image is loaded before I try to display it?
Location: http://www.jguru.com/faq/view.jsp?EID=20617
Created: Mar 6, 2000 Modified: 2000-03-06 19:53:11.004
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

You can use the AWT MediaTracker to start and wait for the loading of an Image object.

Image image = ...;
MediaTracker tracker = new MediaTracker(component or this);
tracker.addImage(image, 0);
try {
  tracker.waitForAll();
} catch (InterruptedException e) {
  System.out.println("Interrupted while loading Image");
}

At this point, if everything went okay, the image would be loaded. You can check the status with statusAll() or statusID() to see if they loaded successfully.

How can I control the Z-order that my overlapping components are drawn in?
Location: http://www.jguru.com/faq/view.jsp?EID=21482
Created: Mar 7, 2000 Modified: 2000-03-13 04:10:50.335
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

AWT does not define z-order behavior. In fact, it is different on different platforms. You would need to draw all the components yourself, instead of relying on the Container to do this for you.

If you are using Swing, you can place your components inside a JLayeredPane and assign each a layer number. Higher layer numbers appear on top of lower layer numbers. (Note that JDesktopPane is a layered pane; each JInternalFrame can be at different layers.)

How can I set multiple lines of text in a Button?
Location: http://www.jguru.com/faq/view.jsp?EID=21664
Created: Mar 8, 2000 Modified: 2000-03-13 04:17:49.02
Author: MAHESH MULCHANDANI (http://www.jguru.com/guru/viewbio.jsp?EID=18395) Question originally posed by Belgundi Achyuth Acharya (http://www.jguru.com/guru/viewbio.jsp?EID=20249

There is no way to set Multiple Lines of Text in an AWT button. If you try to attach a label whose length is more than the width of button it is trimmed on both sides.

You can have multi-line Buttons in Swing, however. The latest version of Swing allows you to specify the button text using HTML, and you can add <br> tags inside the HTML (as well as tags such as <b> and <i>)

How do I create a TextField that limits the number of characters a user can place in it?
Location: http://www.jguru.com/faq/view.jsp?EID=23148
Created: Mar 11, 2000 Modified: 2000-08-03 18:04:43.645
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

To limit the number of characters a user can type into the AWT TextField, you need to watch as the user types and count characters. If the size gets too large, you reject input. You need to still permit characters like TAB for moving focus as well as Backspace/Delete for removing characters. The following program demonstrates this.

import java.awt.*;
import java.awt.event.*;
public class SizedTextField extends TextField {
  private int size;  // size = 0 is unlimited
  public SizedTextField () {
    super("");
    this.size = 0;
    init();
  }
  public SizedTextField (int columns) {
    super(columns);
    this.size = 0;
    init();
  }
  public SizedTextField (int columns, int size) {
    super (columns);
    this.size = Math.max (0, size);
    init();
  }
  public SizedTextField (String text) {
    super(text);
    this.size = 0;
    init();
  }
  public SizedTextField (String text, int columns) {
    super(text, columns);
    this.size = 0;
    init();
  }
  public SizedTextField (String text, int columns, int size) {
    super(text, columns);
    this.size = Math.max (0, size);
    init();
  }
  private void init() {
    KeyListener listener = new KeyAdapter() {
      public void keyPressed(KeyEvent e) {
        int key = e.getKeyCode();
        if ((size > 0) &&
          (((TextField)(e.getComponent())).getText().length () >= size)) {
          // Check for backspace / delete / tab -- let these pass through
          if ((key == KeyEvent.VK_DELETE) || (key == KeyEvent.VK_TAB) || 
              (key == KeyEvent.VK_BACK_SPACE)) {
            return;
          } else {
            e.consume();
          }
        }
      }
    };
    addKeyListener(listener);
  }
  protected String paramString () {
    String str = super.paramString ();
    if (size != 0) {
      str += ",size=" + size;
    }
    return str;
  }
  public static void main(String args[]) {
    Frame f = new Frame("Test");
    TextField tf1 = new TextField();
    TextField tf2 = new SizedTextField(10, 10);
    f.add(tf1, BorderLayout.NORTH);
    f.add(tf2, BorderLayout.SOUTH);
    f.pack();
    f.show();
  }
}

A note of caution. This does not limit you as a programmer from saying setText() with some really long string.

How can I keep a PopupMenu/JPopupMenu visible after I select one of its menu items?
Location: http://www.jguru.com/faq/view.jsp?EID=23340
Created: Mar 12, 2000 Modified: 2000-03-14 10:57:10.822
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by John Zukowski PREMIUM (http://www.jguru.com/guru/viewbio.jsp?EID=7

This is basically what is called a tearoff menu. You would need to simulate the behavior by putting the top level set of menu choices within a Window, providing some way for the user to close the window.

How do I create Menus which are loaded based upon user authentication?
Location: http://www.jguru.com/faq/view.jsp?EID=23341
Created: Mar 12, 2000 Modified: 2000-03-14 10:58:05.886
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Vinay Solanke (http://www.jguru.com/guru/viewbio.jsp?EID=12334

The JFC Notepad demo that comes with the JDK demonstrates how to load menus dymanically. You can setup different locales to define different authorization levels.

How can I find the center of a circle drawn using Graphics.drawArc()?
Location: http://www.jguru.com/faq/view.jsp?EID=23344
Created: Mar 12, 2000 Modified: 2000-03-18 15:24:02.965
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Thomas K Jacob (http://www.jguru.com/guru/viewbio.jsp?EID=16991

The drawArc() method has six arguments: the x and y coordinates of the top left corner, the width and height, as well as the start and ending angle positions. To get the center point, all you need is four of them. The width of the circle is from x to x+width-1. The height of the circle is from y to y+height-1. Thus, the center point would be x+(width-1)/2, y+(height-1)/2.

The minus one is necessary because a starting pixel is at x (or y). This is just like arrays where a 100 element array is indexed from 0 to 99.

How do I print a multi-page text document?
Location: http://www.jguru.com/faq/view.jsp?EID=23346
Created: Mar 12, 2000 Modified: 2000-03-16 07:54:51.412
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by John Zukowski PREMIUM (http://www.jguru.com/guru/viewbio.jsp?EID=7

For Java 1.1, the following program will demonstrate the printing of multi-page documents.

// This example is from the book _Java AWT Reference_ by John Zukowski.
// Written by John Zukowski.  Copyright (c) 1997 O'Reilly & Associates.
// You may study, use, modify, and distribute this example for any purpose.
// This example is provided WITHOUT WARRANTY either expressed or
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.Properties;

public class TestPrint extends Frame {
  TextArea textArea;
  Label statusInfo;
  Button loadButton, printButton, closeButton;
  Properties props = new Properties();
    
  public TestPrint() {
    super ("File Loader");
    add (statusInfo = new Label(), "North");
    Panel p = new Panel ();
    p.add (loadButton = new Button ("Load"));
    loadButton.addActionListener( new LoadFileCommand() );
    p.add (printButton = new Button ("Print"));
    printButton.addActionListener( new PrintCommand() );
    p.add (closeButton = new Button ("Close"));
    closeButton.addActionListener( new CloseCommand() );        
    add (p, "South");
    add (textArea = new TextArea (10, 40), "Center");
    pack();
  }
  public static void main (String args[]) {
    TestPrint f = new TestPrint();
    f.show();
  }

  // Bail Out
  class CloseCommand implements ActionListener {
    public void actionPerformed (ActionEvent e) {
      System.exit (0);
    }
  }
    
  // Load a file into the text area.
  class LoadFileCommand implements ActionListener {
    public void actionPerformed (ActionEvent e) {
      int state;
      String msg;
      FileDialog file = new FileDialog (TestPrint.this, "Load File", FileDialog.LOAD);
      file.setFile ("*.java");  // Set initial filename filter
      file.show(); // Blocks
      String curFile;
      if ((curFile = file.getFile()) != null) {
        String filename = file.getDirectory() + curFile;
        char[] data;
        setCursor (Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
        File f = new File (filename);
        try {
          FileReader fin = new FileReader (f);
          int filesize = (int)f.length();
          data = new char[filesize];
          fin.read (data, 0, filesize);
        } catch (FileNotFoundException exc) {
          String errorString = "File Not Found: " + filename;
          data = errorString.toCharArray ();
        } catch (IOException exc) {
          String errorString = "IOException: " + filename;
          data = errorString.toCharArray ();
        }
        statusInfo.setText ("Load: " + filename);
        textArea.setText (new String (data));
        setCursor (Cursor.getPredefinedCursor(Cursor.DEFAULT_CURSOR));
      }
    }
  }

  // Print a file into the text area.
  class PrintCommand implements ActionListener {
    public void actionPerformed (ActionEvent e) {
      PrintJob pjob = getToolkit().getPrintJob(TestPrint.this, "Cool Stuff", props);
      if (pjob != null) {
        Graphics pg = pjob.getGraphics();
        if (pg != null) {
          String s = textArea.getText();
          printLongString (pjob, pg, s);
          pg.dispose();
        }
        pjob.end();
      }
    }
  }

  // Print string to graphics via printjob
  // Does not deal with word wrap or tabs
  void printLongString (PrintJob pjob, Graphics pg, String s) {
    int pageNum = 1;
    int linesForThisPage = 0;
    int linesForThisJob = 0;
    // Note: String is immutable so won't change while printing.
    if (!(pg instanceof PrintGraphics)) {
      throw new IllegalArgumentException ("Graphics context not PrintGraphics");
    }
    StringReader sr = new StringReader (s);
    LineNumberReader lnr = new LineNumberReader (sr);
    String nextLine;
    int pageHeight = pjob.getPageDimension().height;
    Font helv = new Font("Helvetica", Font.PLAIN, 12);
    //have to set the font to get any output
    pg.setFont (helv);
    FontMetrics fm = pg.getFontMetrics(helv);
    int fontHeight = fm.getHeight();
    int fontDescent = fm.getDescent();
    int curHeight = 0;
    try {
      do {
        nextLine = lnr.readLine();
        if (nextLine != null) {         
          if ((curHeight + fontHeight) > pageHeight) {
            // New Page
            System.out.println ("" + linesForThisPage + " lines printed for page " + 

pageNum);
            pageNum++;
            linesForThisPage = 0;
            pg.dispose();
            pg = pjob.getGraphics();
            if (pg != null) {
              pg.setFont (helv);
            }
            curHeight = 0;
          }
          curHeight += fontHeight;
          if (pg != null) {
            pg.drawString (nextLine, 0, curHeight - fontDescent);
            linesForThisPage++;
            linesForThisJob++;
          } else {
            System.out.println ("pg null");
          }
        }
      } while (nextLine != null);
    } catch (EOFException eof) {
      // Fine, ignore
    } catch (Throwable t) { // Anything else
      t.printStackTrace();
    }
    System.out.println ("" + linesForThisPage + " lines printed for page " + pageNum);
    System.out.println ("pages printed: " + pageNum);
    System.out.println ("total lines printed: " + linesForThisJob);
  }
}

Why should I call repaint() instead of paint()?
Location: http://www.jguru.com/faq/view.jsp?EID=23379
Created: Mar 12, 2000 Modified: 2000-03-16 08:00:51.022
Author: Finlay McWalter (http://www.jguru.com/guru/viewbio.jsp?EID=13911) Question originally posed by sailesh patra (http://www.jguru.com/guru/viewbio.jsp?EID=18223

repaint() enqueues a paint message onto the system's event queue. Later (in another thread) the AWT system will dequeue this message and dispatch it. One of the (many) things it does is call the paint() or update() method of the component. If you directly call paint() yourself, you'll run in to the following issues:

1. You lose serial paint processing
   By doing painting in any old thread you're calling graphics primitives on the same compoent in one thread while the system event thread is potentially calling on the same component them in another thread.
   Thus you run into reentrancy issues in your own code and in AWT, race conditions between your own threads and you greatly increase the probability of lock contention for internal AWT resources, which will be to the detriment of performance. A well-behaved AWT programming does all of its actual painting to real components in response to paint events, inside the system's event handler thread.
2. You lose paint event elision
   The AWT internals contain code that looks for damage/paint events that overlap each other, and tries to glue them together into one big event, which is much more efficient. By circumventing this mechanism you may, in some applications, be unnecessarily repainting the same area of the screen a bunch of times - an AWT that doesn't elide paint events runs much slower in a lot of circumstances.
3. You lose native notification
   By calling repaint() you ensure that the native paint code for the component is called. Just calling paint() yourself stops this from happening - which might cause you problems if you expect the native to be properly painted too.
4. You're breaking the pattern
   From a software-engineering stand-point, you're breaking with the general AWT repaint paradigm. This would be okay if you were gaining some advantage from doing so, but you aren't, so you're unnecessarily making your code less maintainable, harder for others to understand and less reusable.

How can I get the current mouse coordinates while handling a KeyEvent in a keyPressed(KeyEvent) method?
Location: http://www.jguru.com/faq/view.jsp?EID=23383
Created: Mar 12, 2000 Modified: 2000-03-16 08:33:54.893
Author: Finlay McWalter (http://www.jguru.com/guru/viewbio.jsp?EID=13911) Question originally posed by Nils-Gunnar Nilsson (http://www.jguru.com/guru/viewbio.jsp?EID=3199

The KeyEvent doesn't contain that information, but you can do the following:

1. Add both a KeyListener and a MouseMotionListener to the component you're interested in.
2. In the mouseMoved() callback, store the MouseEvent in an instance variable.
3. In the keyPressed() callback, get the last reported location of the mousepointer by calling getPoint() on that MouseEvent you stored.

This will work fine unless you need accurate performance in applications where the mouse is likely to be moving when the key is pressed (e.g. video games) - in which case you'll probably find that the reported mouse position appears to 'lag' the actual mouse pointer.

Can I make setBackground() a Transparent Color?
Location: http://www.jguru.com/faq/view.jsp?EID=23387
Created: Mar 12, 2000 Modified: 2000-03-18 15:24:46.546
Author: Finlay McWalter (http://www.jguru.com/guru/viewbio.jsp?EID=13911) Question originally posed by Darren Dunkley-Smith (http://www.jguru.com/guru/viewbio.jsp?EID=16106

In Java2, sure, the AWT contains a constructor for java.awt.Color that takes an alpha (transparency) value - just set this to 0.

Java 1.1.x doesn't support this, so you can't have a transparent background color.

Can I draw rotated text, without using the Java2D API?
Location: http://www.jguru.com/faq/view.jsp?EID=23388
Created: Mar 12, 2000 Modified: 2000-03-18 15:25:29.131
Author: Finlay McWalter (http://www.jguru.com/guru/viewbio.jsp?EID=13911) Question originally posed by John Zukowski PREMIUM (http://www.jguru.com/guru/viewbio.jsp?EID=7

No, not really.

The only thing you can do is use the regular AWT graphics code to draw into an offscreen image - and then you can rotate the offscreen image yourself - doing so for 90 degree rotations is pretty easy, but for other angles its not so much fun.

How do you eliminate widgets that don't have a traversable property from the tabbing sequence, so that some components on a panel never receive the focus from the tab key?
Location: http://www.jguru.com/faq/view.jsp?EID=23389
Created: Mar 12, 2000 Modified: 2000-03-18 15:26:10.27
Author: Finlay McWalter (http://www.jguru.com/guru/viewbio.jsp?EID=13911) Question originally posed by Greg Joyce (http://www.jguru.com/guru/viewbio.jsp?EID=15123

Override the isFocusTraversible() method (from java.awt.Component) and always return false.

What is double buffering?
Location: http://www.jguru.com/faq/view.jsp?EID=23392
Created: Mar 12, 2000 Modified: 2000-03-18 21:13:33.136
Author: Finlay McWalter (http://www.jguru.com/guru/viewbio.jsp?EID=13911) Question originally posed by John Zukowski PREMIUM (http://www.jguru.com/guru/viewbio.jsp?EID=7

Double-buffering is a technique to reduce flickering in drawing, particularly in animation.

Instead of drawing directly onto the component (in the paint or update method) you create an offscreen image (using component.createImage) and paint your picture into that. Once you're done you actualise the image by painting it onto the graphics context of an actual component - thus there isn't a time when your image can be seen half-drawn.

How do I create a window-less frame to put my applet (applet only no borders)? or is that possible?
Location: http://www.jguru.com/faq/view.jsp?EID=23782
Created: Mar 13, 2000 Modified: 2001-10-29 22:18:38.807
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Zhi Shen (http://www.jguru.com/guru/viewbio.jsp?EID=21324

Anything you do like this would not be from Java. You should be able to do this with JavaScript. http://plutoniumsoftware.com/games/bm3d/ does something similar to what you want, but not exactly.

Note: the question is not about creating an undecorated frame from an applet. It is to load the applet into an undecorated browser window.

How do I show diagrams and graphs?
Location: http://www.jguru.com/faq/view.jsp?EID=25795
Created: Mar 18, 2000 Modified: 2000-03-19 06:33:44.986
Author: Anil Punjabi (http://www.jguru.com/guru/viewbio.jsp?EID=23218) Question originally posed by Kristijan Marin (http://www.jguru.com/guru/viewbio.jsp?EID=15063

You can try JLoox athttp://www.loox.com

There are several other packages available as well. Try searching for "java chart" on the web

[FAQ Manager Note: If you would like to recommend other specific tools, please submit a feedback!]

How do I draw in an off-screen image?
Location: http://www.jguru.com/faq/view.jsp?EID=25812
Created: Mar 18, 2000 Modified: 2000-03-19 06:36:51.274
Author: Finlay McWalter (http://www.jguru.com/guru/viewbio.jsp?EID=13911) Question originally posed by Jean-Yves BRUD (http://www.jguru.com/guru/viewbio.jsp?EID=8908

After you've created the offscreen image, you can draw into it by getting the appropriate Graphics object, which you get by calling getGraphics on the offscreen image. Here's a basic example:

Canvas c = new Canvas();
Image i = c.createImage(10, 10); // create offscreen image
Graphics g = i.getGraphics();
g.drawRect(0,1,2,3); // draw into the offscreen image

How can I determine the color of a pixel displayed in a GUI?
Location: http://www.jguru.com/faq/view.jsp?EID=25973
Created: Mar 19, 2000 Modified: 2000-03-20 14:15:45.512
Author: Andre van Dalen (http://www.jguru.com/guru/viewbio.jsp?EID=7570) Question originally posed by Jean-Yves BRUD (http://www.jguru.com/guru/viewbio.jsp?EID=8908

If you use double buffering, your question comes down to how to determine the pixel color in the image you use to paint to the screen. You can use the PixelGrabber class to tranform (part of) your Image into an int[] and read the pixel color from that.

If you want to determine the color of a pixel on the screen, you need to use JNI to call a C++ routine that retrieves pixels from the screen.

[FAQ Manager note: Double Buffering refers to drawing to an alternate, offscreen image before dumping that image to the screen.]

What are the issues in using Swing along with AWT?
Location: http://www.jguru.com/faq/view.jsp?EID=26294
Created: Mar 20, 2000 Modified: 2000-03-20 14:24:15.235
Author: Joseph Shelby (http://www.jguru.com/guru/viewbio.jsp?EID=26292) Question originally posed by Chakree Chakree (http://www.jguru.com/guru/viewbio.jsp?EID=22927

The article Mixing Heavyweights at the Swing Connection from Javasoft has details on what caveats you need to be aware of in mixing Heavy and Light components together.

How can I display a modal Dialog from an applet in the Browser?
Location: http://www.jguru.com/faq/view.jsp?EID=27423
Created: Mar 22, 2000 Modified: 2001-07-26 21:11:51.245
Author: Finlay McWalter (http://www.jguru.com/guru/viewbio.jsp?EID=13911) Question originally posed by Rajesh Sharma (http://www.jguru.com/guru/viewbio.jsp?EID=26470

In order to display a Dialog, you need a Frame to be the "owner" of the dialog - all of the java.awt.Dialog constructors require a Frame. Now, I've seen several "teach yourself java" books that say you should make a dummy Frame, and then pass that in as the parent - but that's plain silly.

What you need to do is walk up the AWT widget instance heirarchy (walking upward from the applet) - at the top of such heirarchies you'll find a Window, a Dialog or a Frame (the three "toplevel" widgets in AWT) - thoughtfully the applet host code will always set itself up as a Frame, just so you can use that as a parent for your dialogs. This walkup procedure is shown in the following example - it's done in the findParentFrame() method.

 
import java.awt.*; 
import java.awt.event.*; 
import java.applet.Applet; 

public class test extends Applet implements ActionListener { 
  Button b; 

  private Frame findParentFrame(){ 
    Container c = this; 
    while(c != null){ 
      if (c instanceof Frame) 
        return (Frame)c; 

      c = c.getParent(); 
    } 
    return (Frame)null; 
  } 

  public void init(){ 
    setLayout(new FlowLayout()); 
    b = new Button("push me"); 
    b.addActionListener(this); 
    add(b); 
  } 

  public void actionPerformed(ActionEvent e){ 
    Frame f = findParentFrame(); 
    if(f != null){ 
      Dialog d = new Dialog(f, "modalDialog", true); 
      d.setLayout(new FlowLayout()); 
      d.add(new Label("hello")); 
      d.pack(); 
      d.setLocation(100,100); 
      d.show(); 
    } 
  } 
} 

So that's that, right?

Well, not entirely. As with many aspects of their implementation of Java applets, browsers differ in how they interpret the meaning of "modal". Almost all make the dialog modal with respect to the applet that created it, but some make it fully modal (i.e. the entire browser is waiting on the modal dialog) and others allow other browser windows or even the same browser window (perhaps with other Java applets in it) to continue to run. This seems to happen more because of the way browser vendors implement the event handling loops in their products than by deliberate design (one major browser manufacturer we could name varies in this regard between the same browser on different OSes). Short of scary JavaScript/LiveConnect/JNI nastiness, you'll have to live with your browser manufacturer's conception of how to implement modal.

For browser manufacturers, ignoring modal behaviour for applets is often a wise choice - otherwise, malicious or defective applets (um, like my example above) can bring up a modal dialog with no means of it being closed, and thus leave the entire browser unusable - forcing the user to kill the browser to recover.

Another small note about modal dialogs - if you intend your applet to work on Personal Java platforms (things like cable-boxes and webphones) you should assume that only modal dialogs are permitted - Personal Java allows the browser to throw an exception if the browser doesn't support non-modal dialogs.

How do I display an Image in an applet or application?
Location: http://www.jguru.com/faq/view.jsp?EID=28451
Created: Mar 25, 2000 Modified: 2000-09-14 13:10:29.762
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Sunil Varghese (http://www.jguru.com/guru/viewbio.jsp?EID=28026

The basic manner of displaying an Image in an applet/application is to call the drawImage() method of the Graphics class in the paint() method of the component to display the image. There are six varieties of the method that deal with scaling and background colors for transparent images. The basic manner of calling is as follows:

g.drawImage(image, xPosition, yPosition, this);

The last argument is what's called an ImageObserver and helps deal with the asynchronous loading of image data. Generally speaking, you just pass a reference to the applet as the image observer so that as more data is loaded the applet (the observer) is notified and redraws itself.

This leaves one question though. How do you get the image to display? The getImage() method of Applet or Toolkit helps here, requiring just the URL of where to get the image from:

Image image = getImage(url);

For an application, you would instead use getImage() method of Toolkit:

Toolkit kit = Toolkit.getDefaultToolkit();
Image image = kit.getImage(url);
Image image = kit.getImage(filename);

To make matters simpler for an applet, allowing you to move an applet between hosts without having to hardcode where the images come from, you can use a second variety of the method:

Image image = getImage(baseURL, file);

Here, you provide the base URL and filename separately. The two are combined to form the specific URL to get the image file from. How is this better? Well, there are two more methods to help here. The getDocumentBase() method allows you to start with a base URL of where the HTML file is located. And, the getCodeBase() method allows you to start with a base URL of where the .class file is located. Using one of the two you can find an image in the same directory as either with something like this:

Image image = getImage(getDocumentBase(), "image.jpg");

That is basically it, except if you want to package image files into a JAR. For this, you need to use the getResourceAsStream() method of the Class class.

InputStream in = getClass().getResourceAsStream
    ("image.gif");
byte buffer[] = new byte[in.available()];
for (int i = 0, n = in.available(); i<n; i++)
  buffer[i] = (byte)in.read();
// in.read(buffer); 
// this doesn't read all when reading from JAR
Toolkit toolkit = Toolkit.getDefaultToolkit();
Image image = toolkit.createImage(buffer);

Unfortunately, you cannot use the getResource() method (which returns a URL) as Netscape browsers do not support it.

How can I get the component/container structure of an open Window?
Location: http://www.jguru.com/faq/view.jsp?EID=30309
Created: Mar 30, 2000 Modified: 2000-04-03 10:47:07.82
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

Programmatically, you can call the list() method of Component/Container. You can also press CTRL-SHIFT-F1 while the window has the input focus and the structure will be dumped to standard output (System.out).

How can I change the cusror when the mouse button is pressed?
Location: http://www.jguru.com/faq/view.jsp?EID=30964
Created: Apr 1, 2000 Modified: 2000-04-03 11:07:55.353
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by radha gadiraju (http://www.jguru.com/guru/viewbio.jsp?EID=29279

comp.addMouseListener(
  new MouseAdapter() {
    public void mousePressed(MouseEvent me) {
      // If you are using swing you may want to use
      // SwingUtilities.invokeLater(new Runnable {
      //   public void run() {
      comp.setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));

      // This helps sometimes
      Toolkit.getDefaultToolkit().sync();      
    }});

How and why would you use the java.awt.EventQueue?
Location: http://www.jguru.com/faq/view.jsp?EID=31064
Created: Apr 2, 2000 Modified: 2000-04-03 11:18:24.257
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by lyndon mendoza (http://www.jguru.com/guru/viewbio.jsp?EID=8369

Well there are many reasons.

1. Say, you wanted to catch all the mouse events across all the GUI of your application. Without tapping the EventQueue you will have to add a mouse listener and mouse motion listener to every component. You will have to also add container listener to every container so that you can then add mouse listener to newly added components. You will still not know the existence of new frames if it was not explicitly annouced in the program.

2. If you wanted to detect inactivity on the EventQueue so that you could perform low priority background task (like the animation on the help guy in MS word when user seems to be inactive possibly because the user is wondering what to do next etc). You could start a time after every event. If next event comes before the timer expires, restart the timer. If the times expires you know that the event queue has been inactive that long and you could start the background task.

3. You may want to automate the wait cursor as described in a recent article in JavaWorld. Here is the reference - http://www.javaworld.com/javaworld/javatips/jw-javatip87.html

4. The JFC/Swing Accesibility utilities use the event queue to keep track of the GUI state.

5. JavaStar (now discontinued) GUI testing tool used the event queue to keep track of the state of GUI and to do record and playback functionality for regression testing.
   

In fact the AWT engineers realized the importance of such a functionality and in JDK1.2 it is directly supported through

java.awt.Toolkit.getDefaultToolkit().addAWTListener(....)

The event queue class also supports push(EventQueue eq) and pop() APIs so that the users can install their own EventQueue.

In JDK1.1 the only way to hook the EventQueue was to modify the JDK-DIR/lib/awt.properties file and add an entry -

AWT.EventQueueClass=<your-eventqueue-subclass> which is dynamically loaded. This affects all the applications run from that installation though. You could turn on the special functionality using a system property or something though.

How do I cut and paste a Java Image to a an external program like Microsoft Paint?
Location: http://www.jguru.com/faq/view.jsp?EID=31065
Created: Apr 2, 2000 Modified: 2000-04-05 04:11:34.36
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by John Zukowski PREMIUM (http://www.jguru.com/guru/viewbio.jsp?EID=7

As of today - no you can't :( in 100% pure Java. That is because of the following bug and other related bugs - http://developer.java.sun.com/developer/bugParade/bugs/4040183.html

You can do that using JNI though. It can be done on MS Windows platform using the following strategy -

Use the java.awt.image.PixelGrabber class to convert the Java Image into a DIB or BMP format array ( the formats used to transfer images on the MS Windows platform). Then pass it to the JNI function which use the following APIs -

OpenClipboard()
EmptyClipboard()

GlobalAlloc( buffer)
GlobalLock( buffer)
// copy image header and data to the buffer
// you wil have to deal with byte and RGB pixel order here
GlobalUnlock(buffer)

SetClipboardData(buffer)

CloseClipboard()

How may I catch popup trigger events for all the components in a JFrame? I tried using GlassPane but it seems a bit to complicated as one must forward all other mouse events in an consistent manner
Location: http://www.jguru.com/faq/view.jsp?EID=31654
Created: Apr 3, 2000 Modified: 2000-04-04 05:39:07.843
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by David Lilljegren (http://www.jguru.com/guru/viewbio.jsp?EID=29979

If you are using JDK1.2 you could use the

java.awt.Toolkit

public void addAWTEventListener(AWTEventListener listener,
                                long eventMask)

API. You could listen to MOUSE_EVENT_MASK mask. Then check if the source of the event is contained in the JFrame that you are trying to track the isPopupTrigger(). If so then check if mouseEvent.isPopTrigger() and if it is do your thing...

How can I use right-to-left text in a JTextPane?
Location: http://www.jguru.com/faq/view.jsp?EID=31690
Created: Apr 3, 2000 Modified: 2000-04-04 05:45:23.921
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by Samsamoddin Rajaei (http://www.jguru.com/guru/viewbio.jsp?EID=22673

Starting JDK1.2 the java.awt.Component class has the following method

public ComponentOrientation getComponentOrientation()

Retrieve the language-sensitive orientation that is to be used to order the elements or text within this component. LayoutManager and Component subclasses that wish to respect orientation should call this method to get the component's orientation before performing layout or drawing.

[FAQ Manager Note]This will apply the orientation to a single component. If you want to apply it to all components under a Window, use

java.awt.Window.applyResourceBundle()

]

How do I create a modal Dialog without a Titlebar/close button or if that is not possible, how do I create a modal Window?
Location: http://www.jguru.com/faq/view.jsp?EID=32674
Created: Apr 5, 2000 Modified: 2000-04-24 20:56:12.771
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by Josh Marquart (http://www.jguru.com/guru/viewbio.jsp?EID=30693

The following might work

public class YourFrame extends Frame {

  // blah
  // blah

  private void showModalWindow() {
     Window w = new Window(this);
     w.setLayout(new BorderLayout());
     w.add(new Label("Modal Window"), BorderLayout.CENTER);
     w.pack();
     // or w.setBounds() etc.
     w.addWindowListener(
         new WindowAdapter() {
              public void windowClosed(WindowEvent we) {
                 // remove listener
                 we.getWindow().removeWindowListener(this);
                 // enable outer YourFrame instance
                 setEnabled(true); 
              }
         }
     );
     setEnabled(false);
     w.setVisible(true);
  }
}

Can I make frames have curved/rounded borders?
Location: http://www.jguru.com/faq/view.jsp?EID=33025
Created: Apr 6, 2000 Modified: 2000-04-07 07:22:13.487
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by Anil Punjabi (http://www.jguru.com/guru/viewbio.jsp?EID=23218

No, you can't (at least not in 100% pure Java).

How do I add a popup menu to an item in a List(AWT 1.1)?
Location: http://www.jguru.com/faq/view.jsp?EID=33838
Created: Apr 8, 2000 Modified: 2000-04-16 06:52:18.609
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by Christopher MacDougald (http://www.jguru.com/guru/viewbio.jsp?EID=32183

The trick is to figure out what is the index of the item at the mouse press location.

Couple of tricks could be used -

1. Create offscreen (location -2000, -2000) list with 5 items i.e. new List(5). Fill it with 5 items. Call getPreferredHeight() and divide by 100 to get the row height. Once you know the row height rest is easy. Just listen to the mouseEvents. Check for mouseEvent.isPopupTrigger(). Then show the popup based on the index of the item under the mouseEvent.getPoint(). You can even build the popup menu on the fly (not reccommended).
2. If the list is single select. The mouse event should select the item under it. Then do the showing of popup based on getSelectedIndex().

Should I ever use the Java 1.0 event handling mechanisms?
Location: http://www.jguru.com/faq/view.jsp?EID=33993
Created: Apr 9, 2000 Modified: 2000-09-14 07:58:01.13
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by John Zukowski PREMIUM (http://www.jguru.com/guru/viewbio.jsp?EID=7

In most cases, the answer is no. Around 90% of the browsers people use support the Java 1.1 AWT capabilities. However, if you really want to hit 100% and not lock out some users, than you are stuck with the 1.0 world. Of course, this also means that the users are at a security risk, as there have been many security fixes since the older browser releases, for both Java and JavaScript.

[FAQ Manager note] You can also put a note on your web page stating "You need Java 1.1 support to view this applet". The 1.1 browsers have been available for long enough that it's really fair to expect your users to upgrade.

How do I create an new image as part (rectangle) of a source image?
Location: http://www.jguru.com/faq/view.jsp?EID=33997
Created: Apr 9, 2000 Modified: 2000-04-16 07:08:11.887
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Gaetano Gallo (http://www.jguru.com/guru/viewbio.jsp?EID=30091

Look at using the CropImageFilter.

Image image = ...;
ImageFilter filter = new CropImageFilter(x,y,width,height);
Image newImage = createImage(new FilteredImageSource(image.getSource(), filter));

How can I display characters of the symbol font (ex: Arrow symbols... up and down arrows) on an applet?
Location: http://www.jguru.com/faq/view.jsp?EID=35388
Created: Apr 12, 2000 Modified: 2000-06-09 19:36:08.667
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Sandilya Vadapalli (http://www.jguru.com/guru/viewbio.jsp?EID=31317

The symbols have a specific mapping into Unicode. You need to learn what their Unicode position is and use that. For instance, you'll find the arrows from 2190-2195. You'll then have to make sure you are using a font that supports them. For instance, bold Serif does, but plain doesn't. The following program demonstrates how to dipslay the arrows:

import java.awt.*;
import java.applet.Applet;

public class Arrow extends Applet {
  public void paint(Graphics g) {
    g.setFont(new Font("Serif", Font.BOLD, 25));
    g.drawString("\u2190\u2191\u2192\u2193\u2194\u2195", 20, 20);
  }
}

If you would like help in finding characters for different fonts, check out the UnicodeDisplay program in the Java Examples in a Nutshell from O'Reilly at http://www.oreilly.com/catalog/jenut/examples/.

While displaying a font on an applet, is it necessary for the system running the browser to have the font or is it carried across from the web server where the applet resides?
Location: http://www.jguru.com/faq/view.jsp?EID=35416
Created: Apr 12, 2000 Modified: 2001-07-26 21:25:20.358
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Sandilya Vadapalli (http://www.jguru.com/guru/viewbio.jsp?EID=31317

Prior to the 1.3 release, the font was required to be on the user's platform and their font.properties file had to be modified so you could use it. Starting with 1.3, you can call public static Font createFont(int fontFormat, InputStream fontStream) throws FontFormatException, IOException which lets you pass true type fonts across an input stream.

However, Font.createFont() uses a working file to create the new font. And, untrusted applets have no permission to create the working file. Consider creating the Font in a servlet and serializing it back to the applet.

Is it possible to enable Drag & Drop in applets and if so, how?
Location: http://www.jguru.com/faq/view.jsp?EID=35982
Created: Apr 13, 2000 Modified: 2001-07-26 21:30:57.753
Author: Saket Malhotra (http://www.jguru.com/guru/viewbio.jsp?EID=35980) Question originally posed by Jesper Berglund (http://www.jguru.com/guru/viewbio.jsp?EID=11962

You need Java 2 support for the drag & drop APIs. You can obtain this by requiring the Java Plug in for your applet.

The other alternative is to create your own custom drag and drop library

Apparently, you can't create the drop targets in init() or start().

How do I change the color of individual list items in AWT 1.1?
Location: http://www.jguru.com/faq/view.jsp?EID=36071
Created: Apr 13, 2000 Modified: 2000-04-16 13:36:24.228
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Christopher MacDougald (http://www.jguru.com/guru/viewbio.jsp?EID=32183

The List control in AWT does not support this capability. You'll have to either build your own, find someone else who has, or use the Swing JList control.

Can I change the size of the scrollbars in a java.awt.List component?
Location: http://www.jguru.com/faq/view.jsp?EID=36072
Created: Apr 13, 2000 Modified: 2000-04-16 07:18:43.924
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Zhi Shen (http://www.jguru.com/guru/viewbio.jsp?EID=21324

You have no control over the scrollbar size with the List component. Its a native / peer-based control. What the operating system gives you is what you get.

What is a lightweight component?
Location: http://www.jguru.com/faq/view.jsp?EID=38532
Created: Apr 20, 2000 Modified: 2000-05-20 17:55:29.245
Author: Tim Rohaly (http://www.jguru.com/guru/viewbio.jsp?EID=10)

Before talking about lightweight components, it is necessary to discuss the concept of Java peers. When instantiating any of the AWT component classes, e.g. a java.awt.Button, the system actually asks the native environment to create the component. This ensures the user sees the native look-and-feel and the component acts like the native control. The native code that provides this look-and-feel is called a peer; each platform has its own set of peers. A Java button appears and acts as a Windows button when run under Windows, as a Macintosh button when run under Macintosh, and as a Unix button when run under Unix. The FAQ found at http://www.jguru.com/jguru/faq/view.jsp?EID=11353 discusses the concept of peers in more detail.

While in practice this sounds great, there are problems because not all native controls respond similarly to the same events. This can result in a Java program exhibiting different behavior under different Java AWT environments. To overcome this problem, you must use components written entirely in Java. That is, components that do not have a native peer. These are called lightweight components. Swing provides a set of pure Java lightweight components, ensuring better cross-platform compatibility. (Or at least ensuring that any bugs are the same bugs on all platform - a very important feature!)

A lightweight component is one that subclasses java.awt.Component (or java.awt.Container) directly - implementing the look-and-feel of the component in Java rather than delegating the look-and-feel to a native peer. Lightweight components can be more efficient at utilizing system resource, they can be transparent, and they do not have to be rectangular (all of which are limitations when working with components that have a peer). For instance, if you are creating lots of panels to help layout components, you can create a LightweightPanel class that subclasses Container to use instead. This would allow you to use the LayoutManager on your panel but not require the overhead of managing all the heavyweight peers that would be created with each java.awt.Panel.

How can I create my own component?
Location: http://www.jguru.com/faq/view.jsp?EID=38533
Created: Apr 20, 2000 Modified: 2000-04-24 20:29:49.564
Author: Tim Rohaly (http://www.jguru.com/guru/viewbio.jsp?EID=10) Question originally posed by sudhakar ks (http://www.jguru.com/guru/viewbio.jsp?EID=26574

To create an actual component that is lightweight requires six steps:

• You need to define a constructor or constructors in order to initialize the state of your component If your component is to respond to any events internally (like mouse presses to activate it), this has to be enabled in the constructor, usually by adding the appropriate listener.
• Assuming that in the previous step you added a listener for handling internal events, you have to now define the listener class. It is best to do this with an inner class because then access is restricted to the lightweight component.
• You need to deal with sizing the object and programmatically changing any properties. For instance, if you have a button that supports changing of its label, you also need to provide a method to recalculate its size when the label is changed.
• You need to override the paint() method so the component can be drawn. This is where you define the visual appearance of your component.
• If you want your component to be non-rectangular, you need to override the contains() method. The contains() method should return true when it is over an area of the object. This routine should be very fast as it will be called frequently. By default, it always returns true. If your component is defined by a java.awt.Polygon shape, that class has a contains() method that you can call. Otherwise, you have to calculate this yourself.
• If you plan on supporting the notification of objects when an event happens (like sending an java.awt.event.ActionEvent when a button is selected, you need to create add/removeXXXListener() methods. Assuming the event type you are using is one of the predefined AWT events, you can use the java.awt.AWTEventMulticaster class to add and remove listeners from the list.

And that's all there is to it.

The following source demonstrates all this by creating a round button component. This component is activated only if selected within the circle. The code is simplified to illustrate the important points when creating your own component - if you want this to behave like a real button then you will have to get more sophisticated with the mouse event handling. First, the constructor initializes the radius and creates a listener for mouse events:

import java.awt.*;
import java.awt.event.*;

public class CircularButton extends Component {

    private int radius;
    boolean pressed = false;
    ActionListener actionListener = null;


    public CircularButton() {
        this(5);
    }

    public CircularButton(int radius) {
        if (radius < 0) {
            throw new IllegalArgumentException("Illegal Radius: " + radius);
        }
        this.radius = radius;
        addMouseListener(new ClickAdapter());
        setSize(getPreferredSize());
    }

This component is the source of ActionEvents, like all buttons, so it is responsible for maintaining a list of listeners and providing methods to add and remove listeners. It does this with the help of the java.awt.AWTEventMulticaster class:

    public void addActionListener(ActionListener l) {
        actionListener = AWTEventMulticaster.add(actionListener, l);
    }

    public void removeActionListener(ActionListener l) {
        actionListener = AWTEventMulticaster.remove(actionListener, l);
    }

The constructor defined an inner class called ClickAdapter to handle mouse events. This event handler doesn't worry if the mouse click is over the object or not, it just keeps track of the state of pressed and notifies the listeners. Because the adding and removing of listeners is done with AWTEventMulticaster, invoking the notification method on the actionListener instance variable (which is actually an instance of AWTEventMulticaster) will notify all the listeners. (If you do not use AWTEventMulticaster, you would need to maintain the listener list in something like a java.util.Vector then iterate through the list of listener elements yourself, calling each listener method. And do it in a thread-safe manner, which AWTEventListener does for you.) ClickAdapter looks like this:

    private final class ClickAdapter extends MouseAdapter {
        public void mousePressed(MouseEvent e) {
            if (isEnabled()) {
                pressed = true;
                repaint();
            }
        }

        public void mouseReleased(MouseEvent e) {
            if (isEnabled()) {
                pressed = false;
                repaint();
                if (actionListener != null) {
                    actionListener.actionPerformed(
                        new ActionEvent(CircularButton.this,
                                        ActionEvent.ACTION_PERFORMED, ""));
                }
            }
        }
    }

There are three sizing routines that need to be overridden so that the layout managers can properly size and position this component:

    public Dimension getPreferredSize() {
        int side = radius *2;
        return new Dimension(side, side);
    }

    public Dimension getMinimumSize() {
        return getPreferredSize();
    }

    public Dimension getMaximumSize() {
        return getPreferredSize();
    }

To draw the component, you must override the paint() method. This is an important step because it defines the visual appearance of your component; an appearance that may even vary with the component's state, as does this button:

    public void paint(Graphics g) {
        super.paint(g);
        if (isEnabled()) {
            if (pressed) {
                g.setColor(Color.white);
                g.fillOval(0, 0, radius*2, radius*2);
                g.setColor(Color.black);
                g.drawOval(0, 0, radius*2, radius*2);
            }
            else {
                g.setColor(Color.black);
                g.fillOval(0, 0, radius*2, radius*2);
            }
        }
        else {
            g.setColor(Color.gray);
            g.fillOval(0, 0, radius*2, radius*2);
        }
    }

Next, override the contains() method in order to support a non-rectangular component. To check to see if a point is within the circle, compare against the radius. Note that the range of the x and y input parameters covers the full size of the circle, and nothing more.

    public boolean contains(int x, int y) {
        //distance = square root of (deltaX squared + deltaY squared)
        int deltax = x - radius;
        int deltay = y - radius;
        double distance = Math.sqrt(Math.pow(deltax, 2) + Math.pow(deltay, 2));
        return (distance <= radius);
    }

Finally, a main method is provided which simply creates a frame with several instances of CircularButton for test purposes:

    public static void main(String[] args) {
        final CircularButton cb1, cb2, cb3, cb4, cb5;
        Frame f = new Frame();
        f.addWindowListener(
            new WindowAdapter() {
                public void windowClosing(WindowEvent e) {
                    System.exit(0);
                }
            }
        );
        f.setLayout(new FlowLayout());
        f.add(cb1 = new CircularButton(25));
        f.add(cb2 = new CircularButton(25));
        f.add(cb3 = new CircularButton(25));
        f.add(cb4 = new CircularButton(25));
        f.add(cb5 = new CircularButton(25));
        ActionListener al = new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                Object o = e.getSource();
                String msg;
                if (o.equals(cb1)) {
                    msg = "One";
                }
                else if (o == cb2) {
                    msg = "Two";
                }
                else if (o == cb3) {
                    msg = "Three";
                }
                else if (o == cb4) {
                    msg = "Four";
                }
                else if (o == cb5) {
                    msg = "Five";
                }
                else {
                    msg = "Huh?" + o;
                }
                System.out.println("Button: " + msg);
            }
        };
        cb1.addActionListener(al);
        cb2.addActionListener(al);
        cb3.addActionListener(al);
        cb4.addActionListener(al);
        cb5.addActionListener(al);
        cb5.setEnabled(false);
        f.pack();
        f.show();
    }
}

How do you make a JavaBean which has a static size?
Location: http://www.jguru.com/faq/view.jsp?EID=39608
Created: Apr 24, 2000 Modified: 2001-07-24 10:28:25.884
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Asim Raja (http://www.jguru.com/guru/viewbio.jsp?EID=24654

To make a fixed size component, just override the getMinimum/Preferred methods to return the fixed size. You should also provide the bean with its own BeanInfo class to effectively hide the size properties. That way, they won't appear. You may find it necessary to update the deprecated methods, too, like preferredSize(), but that shouldn't be necessary. See the Juggler bean that comes with the BDK for one such fixed size component.

If you're class isn't a subclass of Component, all this is irrelevant.

How do I cut and past text from the clipboard?
Location: http://www.jguru.com/faq/view.jsp?EID=39779
Created: Apr 24, 2000 Modified: 2000-04-24 22:21:01.476
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

Starting with Java 1.1, access to the system clipboard is available via the java.awt.datatransfer package. This package also provides the basis for drag-and-drop capabilities, which is included with Java in the 1.2 release (in the java.awt.dnd package).

The Clipboard class is the basis for the capabilities. By asking the Toolkit, you can access the system clipboard with the Toolkit.getSystemClipboard() method. This requires a check past the SecurityManager so is usually restricted within applets. In both applets and applications you can create a Clipboard independent of the system clipboard by just calling the constructor for Clipboard. This way, applets can still provide cut-and-paste capabilities internally, without accessing the system's clipboard, and applications can maintain a private clipboard as well as accessing the system clipboard.

Items are placed on the clipboard with the Clipboard.setContents() method. This requires that the items implement the Transferable interface.

public interface Transferable {
  public abstract DataFlavor
    getTransferDataFlavors()[];
  public abstract boolean
    isDataFlavorSupported(DataFlavor);
  public abstract Object
    getTransferData(DataFlavor);
}
      

The Transferable interface works with items that can be represented in different DataFlavors. Essentially, flavors are MIME types and may be represented by the standard MIME type strings. The getTransferDataFlavors() method returns flavors ordered from richest to simplest (i.e., MS Word, RTF, ASCII). Also, an additional MIME type was introduced to represent Java classes:

application/x-java-serialized-object; class=classname
application/x-java-serialized-object; class=java.util.Vector
      

Because transferring text is so common, Java provides the StringSelection class to assist. There is one limitation with information sent to the system clipboard: between Java programs and non-Java programs, you can only transfer text strings.

Clipboard Access Example

The following program demonstrates the use of all these classes. If there is a command line argument, it places it on the clipboard. Then, it takes off whatever is on the clipboard, as a String, and prints it out. If the contents cannot be represented as a String the exception message String is caught and displayed.

import java.awt.Toolkit;
import java.awt.datatransfer.*;
public class clip {
  public static void main (String args[]) {
    Clipboard clipboard = 
      Toolkit.getDefaultToolkit().getSystemClipboard();
    if (args.length != 0) {
      StringSelection data =
        new StringSelection (args[0]);
      clipboard.setContents (data, data);
    }
    Transferable clipData = 
      clipboard.getContents(clipboard);
    String s;
    try {
      s = (String)(clipData.getTransferData(
        DataFlavor.stringFlavor));
    } catch (UnsupportedFlavorException ee) {
      s = ee.toString();
    }
    System.out.println ("Clipboard Had: " + s);
    System.exit (0);
  }
}

Is it possible to create a tree component using AWT?
Location: http://www.jguru.com/faq/view.jsp?EID=40253
Created: Apr 25, 2000 Modified: 2000-04-29 11:35:28.708
Author: Nicola Ken Barozzi (http://www.jguru.com/guru/viewbio.jsp?EID=39153) Question originally posed by vikram godboley (http://www.jguru.com/guru/viewbio.jsp?EID=37645

Yes, but you are on your own for the drawing.
Matthew Wilson has a free tre implementation in AWT at http://www.bluemoon.net/~mewilson/..

How do I composite(render) 3 images into one image with jdk1.1?
Location: http://www.jguru.com/faq/view.jsp?EID=40932
Created: Apr 26, 2000 Modified: 2000-10-19 05:52:38.561
Author: Rob Edmondson (http://www.jguru.com/guru/viewbio.jsp?EID=35309) Question originally posed by Rok Lee (http://www.jguru.com/guru/viewbio.jsp?EID=20592

Each Image object has a Graphics object. You can modify an Image by using its Graphics object. Create a blank Image, then use its getGraphics() member to obtain its Graphics object. Use this object in the same way you would use the one provided by paint().

Sample Code:

public void paint(Graphics g)	//g is your object's display surface.
{
  //Create & load images once in start() or init() for speed.
  Image imTarget app.createImage(TARGET_WIDTH,TARGET_HEIGHT); 
  Image imSrc1 = app.getImage(app.getCodeBase(), "Image1.jpg");
  Image imSrc2 = app.getImage(app.getCodeBase(), "Image2.jpg");
  Image imSrc3 = app.getImage(app.getCodeBase(), "Image3.jpg");
  int imSrc1_X=0, imSrc2_X=0, imSrc3_X=0, 
      imSrc1_Y=0, imSrc2_Y=0, imSrc3_Y=0;

  Graphics tg = null;
  try {
    tg=imTarget.getGraphics();//Create a render surface.
  }

  catch(Exception e) {
    System.out.println("Error creating render surface" + e);
    return;
  }

  if(imSrc1!=null)
    tg.drawImage(imSrc1, imSrc1_X, imSrc1_Y, this);
    if(imSrc2!=null)
      tg.drawImage(imSrc2, imSrc2_X, imSrc2_Y, this);
    if(imSrc3!=null)
      tg.drawImage(imSrc3, imSrc3_X, imSrc3_Y, this);
    g.drawImage(imTarget,0,0,this);
}

Is the paint method supposed to constantly be called in a JPanel? Is there a way to stop it?
Location: http://www.jguru.com/faq/view.jsp?EID=42529
Created: Apr 30, 2000 Modified: 2000-05-02 07:55:56.255
Author: Nicola Ken Barozzi (http://www.jguru.com/guru/viewbio.jsp?EID=39153) Question originally posed by Clarence Robinson (http://www.jguru.com/guru/viewbio.jsp?EID=22627

First of all, why would you want to stop paint() from being called in a graphical component?

If you do it nothing will be drawn. Unless, of course, you call it on your own, but why stopping something to create something else that does the same thing, and in a standard and consistent way between components?

Usually you deal with paint() and the methods that call it for performance reasons or to eliminate flickering. For the first part performance is rarely on the paint side, and if it is you don't eliminate paint(). As for flickering as you will see in a moment things can be done quite easily.

Maybe you think that paint(), being called continuously, can bog down your app speed; it is not so, because it is not called continuously but only when needed by the window manager (for example resizes, windows overlapping, etc.) or by you, when you do animations.

Let's start by looking at the class Component; Panel extends Component, an uses the paint system written in Component. The following considerations are for all classes that extend Component directly or indirectly. The code is from the source code of the Java classes V1.2.2.

/**
 * Paints this component.  This method is called when the contents
 * of the component should be painted in response to the component
 * first being shown or damage needing repair.  The clip rectangle
 * in the Graphics parameter will be set to the area which needs
 * to be painted.
 * @param g The graphics context to use for painting.
 * @see       java.awt.Component#update
 * @since     JDK1.0
 */
public void paint(Graphics g) {
}

As you can see paint does nothing.

By searching "paint(" in the file you can find that paint() is called by the following methods:

update()
paintAll()
print()

Let's see update:

/**
 * Updates this component.
 * 
 * The AWT calls the update method in response to a
 * call to repaint. The appearance of the
 * component on the screen has not changed since the last call to
 * update or paint. You can assume that
 * the background is not cleared.
 * 
 * The update method of Component
 * does the following:
 * 
 * - Clears this component by filling it 
 *     with the background color.
 * - Sets the color of the graphics context to be
 *     the foreground color of this component.
 * - Calls this component's paint 
 *     method to completely redraw this component.
 *
 * The origin of the graphics context, its
 * (0, 0) coordinate point, is the
 * top-left corner of this component. The
 * clipping region of the
 * graphics context is the bounding rectangle
 * of this component.
 * @param g the specified context to use for updating.
 * @see java.awt.Component#paint
 * @see java.awt.Component#repaint()
 * @since JDK1.0
 */
public void update(Graphics g) {
  if ((this instanceof java.awt.Canvas) ||
      (this instanceof java.awt.Panel) ||
      (this instanceof java.awt.Frame) ||
      (this instanceof java.awt.Dialog) ||
      (this instanceof java.awt.Window)) {

    g.clearRect(0, 0, width, height);
  }
  paint(g);
}

As is stated in the documentation of the method, update() is called by repaint().

In the code you see that it Sets the color of the graphics context to be the foreground color of this component. Calls this component's paint method to completely redraw this component.

To eliminate flickering usually you only need to write a class that extends Component (or any other class that inherits directly or indirectly from it like Panel) with this method:

public void update(Graphics g) {
  paint(g);
}

Flickering is created by the continuous alternation of the animation frames and foreground-colored rectangles, and with the above code you don't draw the rectangle any more.

Here is paintAll():

/**
 * Paints this component and all of its subcomponents.
 * 
 * The origin of the graphics context, its
 * (0, 0) coordinate point, is the
 * top-left corner of this component. The clipping region of the
 * graphics context is the bounding rectangle of this component.
 * @param g the graphics context to use for painting.
 * @see java.awt.Component#paint 
 * @since JDK1.0
 */
public void paintAll(Graphics g) {
  ComponentPeer peer = this.peer;
  if (visible && (peer != null)) {
    validate();
    if (peer instanceof java.awt.peer.LightweightPeer) {
      paint(g);
    } else {
      peer.paint(g);
    }
  }
}

It calls paint only with a java.awt.peer.LightweightPeer.

Here is print():

/**
 * Prints this component. Applications should override this method
 * for components that must do special processing before being
 * printed or should be printed differently than they are painted.
 * 
 * The default implementation of this method calls the
 * paint method.
 * 
 * The origin of the graphics context, its
 * (0, 0) coordinate point, is the
 * top-left corner of this component. The clipping region of the
 * graphics context is the bounding rectangle of this component.
 * @param g the graphics context to use for printing.
 * @see java.awt.Component#paint(java.awt.Graphics)
 * @since JDK1.0
 */
public void print(Graphics g) {
paint(g);
}

print() just calls paint(). From these three methods you can see that to totally eliminate calls to paint() you just need to write a class that extends Component (or any other class that inherits directly or indirectly from it like Panel) with theses methods:

public void update(Graphics g) {
}

public void paintAll(Graphics g) {
  ComponentPeer peer = this.peer; 
  if (visible && (peer != null)) {
    validate();
  if (!(peer instanceof java.awt.peer.LightweightPeer)) {
    peer.paint(g); 
  }
}

public void print(Graphics g) {}

This way paint() never gets called.

By the way it is interesting to see that you can make print() call another method; in this way the printed components can differ visually from the one seen on the screen!

Now let's get back to repaint() that calls update. In fact paint() doesn't get called in the code above but update() does, even if it is empty, by repaint().
You can also see that all other methods in Component call only repaint().

Here is repaint():

/**
 * Repaints this component. 
 *
 * This method causes a call to this component's update
 * method as soon as possible. 
 * @see java.awt.Component#update(java.awt.Graphics)
 * @since JDK1.0 
 */ 
public void repaint() {
  /* getToolkit().getEventQueue().
         removeSourceEvents(this,PaintEvent.PAINT); */ 
  repaint(0, 0, 0, width,
  height);
}

It says that it calls update() but the method is not there!
The getToolkit().getEventQueue().removeSourceEvents(this, PaintEvent.PAINT) removes any pending events for the specified source object (from the EventQueue documentation).

So let' see the other repaint:

/**
 * Repaints the specified rectangle of this component within 
 * tm milliseconds. 
 * 
 * This method causes a call to this component's 
 * update method. 
 * @param tm maximum time in milliseconds before update. 
 * @param x the x coordinate. 
 * @param y the y coordinate. 
 * @param width the width. 
 * @param height the height. 
 * @see java.awt.Component#update(java.awt.Graphics)
 * @since JDK1.0 
 */
public void repaint(long tm, int x, int y, int width, int height) {
  if (this.peer instanceof java.awt.peer.LightweightPeer) {
    // Needs to be translated to parent coordinates since 
    // a parent native container provides the actual repaint 
    // services. Additionally, the request is restricted to 
    // the bounds of the component. 
    int px = this.x + ((x < 0) ? 0 : x); 
    int py = this.y + ((y < 0) ? 0 : y);
    int pwidth = (width > this.width) ? this.width : width; 
    int pheight = (height > this.height) ? this.height : height; 
    parent.repaint(tm, px, py, pwidth, pheight); 
  }
  else { 
    ComponentPeer peer = this.peer; 
    if ((peer != null) && (width > 0) && (height > 0)) {
      peer.repaint(tm, x, y, width, height); 
    }
  }
}

Here you see that it is the peer that calls the update() method; repaint just asks AWT to schedule a call to update(). Anyway, to block repaint do it like is done before with update(), paintAll(), print().

For more information on the AWT methods, how they work and on how to eliminate flickering see the AWT and Swing Tutorials at http://www.javasoft.com/tutorial

How can i get the Handle (HWND) of a java.awt.Canvas on Windows NT/98?
Location: http://www.jguru.com/faq/view.jsp?EID=44507
Created: May 4, 2000 Modified: 2000-05-06 07:43:21.629
Author: Davanum Srinivas (http://www.jguru.com/guru/viewbio.jsp?EID=2011)

import java.awt.*;
import sun.awt.*;

/* This class uses undocumented features of Sun's JDK  */
/* Works only on Windows NT/98 with JDK1.1.8, JDK1.2.2 */
public class SunCanvas extends Canvas
{
    /* Returns the HWND for canvas. */
    public int getHWND() 
    {
        DrawingSurfaceInfo drawingSurfaceInfo;
        Win32DrawingSurface win32DrawingSurface;
        int hwnd = 0;
     
        /* Get the drawing surface */   
        drawingSurfaceInfo =
            ((DrawingSurface)(getPeer())).getDrawingSurfaceInfo();
        
        if (null != drawingSurfaceInfo) {
            drawingSurfaceInfo.lock();
            /* Get the Win32 specific information */
            win32DrawingSurface = 
                 (Win32DrawingSurface)drawingSurfaceInfo.getSurface();
            hwnd = win32DrawingSurface.getHWnd();
            drawingSurfaceInfo.unlock();
        }
        return hwnd;
    }
}

How can I open an HTML page inside a Frame?
Location: http://www.jguru.com/faq/view.jsp?EID=44582
Created: May 4, 2000 Modified: 2000-05-06 07:49:47.381
Author: Davanum Srinivas (http://www.jguru.com/guru/viewbio.jsp?EID=2011) Question originally posed by Rajat Mehta (http://www.jguru.com/guru/viewbio.jsp?EID=42868

If you are willing to use Microsoft Specific Code look at the following article. http://codeguru.developer.com/java/articles/290.shtml

If you want platform independence, you can try JavaSoft's HotJava HTML Component 1.1.2 http://java.sun.com/products/hotjava/#bean

Or you can try ICESoft's ICE Browser http://www.icesoft.no/ICEBrowser/

Why doesn't dispatchEvent(KeyEvent e) work in applets but does in applications?
Location: http://www.jguru.com/faq/view.jsp?EID=45465
Created: May 6, 2000 Modified: 2001-07-26 21:35:35.91
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by lyndon mendoza (http://www.jguru.com/guru/viewbio.jsp?EID=8369

This is actually the result of differences in Java runtime implementations between browser vendor. Microsoft seems to have implemented their event dispatching mechanism differently than the rest of the world. Sun's and Netscape's versions will use dispatchEvent() properly from an applet. You can try out the following test case and see for yourself:

// <applet code=TestCase width=500 height=200>
// </applet>

import java.applet.*;
import java.awt.*;
import java.awt.event.*;

public class TestCase extends Applet {

  TextField t1 = new TextField(50);
  TextField t2 = new TextField(50);

  public void init() {
    add(t1);
    add(t2);
    t1.addKeyListener(new KeyAdapter() {
      public void keyTyped(KeyEvent e) {
        t2.dispatchEvent(e);
      }
    });
  }
}

How do I get focus on a particular component on the screen. I tried requestFocus(), but it did not work. Do I have to do something special to be able to use requestFocus() method on a Button, or a TextField?
Location: http://www.jguru.com/faq/view.jsp?EID=45866
Created: May 8, 2000 Modified: 2000-05-16 21:32:44.072
Author: Simon Brown (http://www.jguru.com/guru/viewbio.jsp?EID=44588) Question originally posed by R Singh (http://www.jguru.com/guru/viewbio.jsp?EID=41413

The requestFocus() method will only work when the component is visible so ensure that your window/applet is visible and that your component has been added to it. Then call the requestFocus() method on the component to switch the focus.

What is the difference between a Component and an Object?
Location: http://www.jguru.com/faq/view.jsp?EID=49214
Created: May 15, 2000 Modified: 2000-05-16 11:06:51.115
Author: Nicola Ken Barozzi (http://www.jguru.com/guru/viewbio.jsp?EID=39153) Question originally posed by Tennneti Narahari (http://www.jguru.com/guru/viewbio.jsp?EID=37338

A Component is a particular type of Object.

This is what the standard Sun documentation says (JDK 1.2.2):

public abstract class Component
extends Object
implements ImageObserver, MenuContainer, Serializable

A component is an object having a graphical representation that can be displayed on the screen and that can interact with the user. Examples of components are the buttons, checkboxes, and scrollbars of a typical graphical user interface.

The Component class is the abstract superclass of the nonmenu-related Abstract Window Toolkit components. Class Component can also be extended directly to create a lightweight component. A lightweight component is a component that is not associated with a native opaque window.

Is there any way to create a full-screen (non-windowed) application in Java?
Location: http://www.jguru.com/faq/view.jsp?EID=53106
Created: May 21, 2000 Modified: 2000-06-29 15:13:58.849
Author: Nicola Ken Barozzi (http://www.jguru.com/guru/viewbio.jsp?EID=39153) Question originally posed by Thijs Stalenhoef (http://www.jguru.com/guru/viewbio.jsp?EID=31863

Yes and no.

Yes because Java has components that are non-windowed. Ironically these are called Window (AWT) and JWindow (Swing).

No because in Microsoft Windows the "Start bar" remains top-level and overlaps with your Window.

Other platforms may have the same problem. Note that you may be able to get a truly full-screen application by using JNI to call native methods on your platform, but that kills portability of your application.

Here is the AWT code to make a Window as large as the screen.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class FullscreenWindowApp extends Window {
  private Button button;

  public FullscreenWindowApp() {
    super(new Frame());
    button = new Button("Close");

    button.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        System.exit(0);
      }});

    setLayout(new FlowLayout());
    add(button);

    //get the screen size
    Dimension screenSize = 
        Toolkit.getDefaultToolkit().getScreenSize();

    //sets the location of the window to top left of screen
    setBounds(0,0,screenSize.width, screenSize.height);
  }

  public static void main(String[] args) {
    new FullscreenWindowApp().setVisible(true);
  }

}

The Swing code is nearly the same, using JWindow instead of Window,

I have a JTextField with more then one FocusListener. If the first-called focusLost fails (for validation), how can I stop the next focusLost call?
Location: http://www.jguru.com/faq/view.jsp?EID=53150
Created: May 21, 2000 Modified: 2000-05-21 08:08:19.818
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by Sachin Shah (http://www.jguru.com/guru/viewbio.jsp?EID=50956

Be very careful on this type of behavior...

First, listeners are intended to be completely independent of each other. There are two main reasons for this:

• A problem in one listener should not impact another listener
• The order of listener calls is not defined by the JavaBean specification

There are two exceptions to this rule:

1. Constrained properties in a JavaBean talk to VetoableChangeListeners. The order of called listeners is not defined, but if any listener throws a PropertyVetoException, the remaining ones are not called.
2. If you write your own events (under the Beans model, same type of pattern as existing AWT events), their behavior is defined by you. You can implement and document that they have a certain order or will stop when any listeners throw an exception.

   I strongly recommend against this as it's not normal behavior for event handling

Note that you cannot simply make the text property constrained. The problem is that the setText method for a constrained JTextField could throw a PropertyVetoException, which isn't declared in the setText method of JTextField.

There are really two things you can do here:

1. You could write a custom event for this, and implement/document that it calls listeners in the added order and that if any throw an exception, the others are not called.
2. Add a single focusLost listener that does the multiple validations in order, stopping if any fail.

I'd recommend the second approach, like the following:

JTextField f = new JTextField();
f.addFocusListener(new FocusListener() {
  public void focusGained(FocusEvent e) {}
  public void focusLost(FocusEvent e) {
    try {
      validation1();
      validation2();
      validation3();
    }
    catch(Exception e) {
      // report the validation error
    }
  }
});

If any of the validations fail (throw an exception), the others are not processed.

Finally, Don't forget that a call to setText() can change the value of the field!. You should override setText() and include validation as well.

How do I create a borderless Frame/JFrame?
Location: http://www.jguru.com/faq/view.jsp?EID=53155
Created: May 21, 2000 Modified: 2000-05-21 08:15:37.284
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by arun prathap (http://www.jguru.com/guru/viewbio.jsp?EID=43168

Instead of using a Frame/JFrame, use Window/JWindow.

The Window/JWindow classes (AWT/Swing) are borderless windows. Frame/JFrame are extensions of Window/JWindow that add borders, a titlebar, and the close/maximize/minimize controls found on most platforms.

How do I load a GIF file into a BufferedImage?
Location: http://www.jguru.com/faq/view.jsp?EID=53328
Created: May 21, 2000 Modified: 2000-05-23 09:02:20.763
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Alberto Lopez (http://www.jguru.com/guru/viewbio.jsp?EID=49150

To load a GIF into a BufferedImage, load the Image normally, get its size, then create an empty BufferedImage of the appropriate size and draw the Image into the buffered image's Graphics context.

The following demonstrates this:

import java.awt.*;
import java.awt.image.*;
import javax.swing.*;

public class BuffIt {
  public static void main (String args[]) {
    // Get Image
    ImageIcon icon = new ImageIcon(args[0]);
    Image image = icon.getImage();

    // Create empty BufferedImage, sized to Image
    BufferedImage buffImage = 
      new BufferedImage(
          image.getWidth(null), 
          image.getHeight(null), 
          BufferedImage.TYPE_INT_ARGB);

    // Draw Image into BufferedImage
    Graphics g = buffImage.getGraphics();
    g.drawImage(image, 0, 0, null);

    // Show success
    JFrame frame = new JFrame();
    JLabel label = new JLabel(new ImageIcon(buffImage));
    frame.getContentPane().add(label);
    frame.pack();
    frame.show();
  }
}

How do I minimize a Java application window?
Location: http://www.jguru.com/faq/view.jsp?EID=53754
Created: May 22, 2000 Modified: 2000-05-23 08:56:49.783
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by Amol Sant (http://www.jguru.com/guru/viewbio.jsp?EID=45958

Assumming you are using a java.awt.Frame or a subclass (including Swing's JFrame) as the Application Window, JDK1.2's java.awt.Frame class has the following method

public void setState(int state)
  Sets the state of this frame.
  Parameters:
    state - Frame.ICONIFIED if this frame is in iconic state;
            Frame.NORMAL if this frame is in normal state.

Use the Frame.ICONIFIED value to minimize it.

How can I save an Image into a file with a standard image format like GIF or JPG?
Location: http://www.jguru.com/faq/view.jsp?EID=57055
Created: May 28, 2000 Modified: 2000-05-28 07:58:09.997
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by Visesh S. V. (http://www.jguru.com/guru/viewbio.jsp?EID=36836

Once you have the Image object, for JPEG you can use

• http://java.sun.com/products/jdk/1.2/docs/guide/2d/api-jpeg/overview-summary.html

and for GIF you can use

• http://www.vsms.nottingham.ac.uk/vsms/java/jumbo/api/jumbo.simplegraph.GIFEncoder.html or
• http://www.research.att.com/~john/Grappa/docs/att.grappa.GIFEncoder.html

Can I prevent the mouse from moving out of a Dialog or Frame?
Location: http://www.jguru.com/faq/view.jsp?EID=58813
Created: May 28, 2000 Modified: 2000-05-28 08:21:31.919
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by G.Shankar Narayanan (http://www.jguru.com/guru/viewbio.jsp?EID=29514

You can't. Standard Java provides no controls to limit where the mouse can go.

I include a JPanel with a null layout in a JScrollPane, and it doesn't display the scrollbars. Why?
Location: http://www.jguru.com/faq/view.jsp?EID=58838
Created: May 28, 2000 Modified: 2000-05-28 08:36:31.631
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by muralidhar reddy gandham (http://www.jguru.com/guru/viewbio.jsp?EID=45444

First, always use layout managers when constructing a GUI! See Effective Layout Management (http://developer.java.sun.com/developer/onlineTraining/GUI/AWTLayoutMgr) for details on why, what layout managers are and how to use them.

Second, a JScrollPane asks the contained component for its preferred size. A JPanel with no layout manager returns (0,0), which tells the JScrollPane that it doesn't need to provide scrollbars.

A JPanel with a layout manager delegates the preferred size request to its layout manager, which computes a size that should make all the contained components happy. When this, (usually) non-zero size is returned, the JScrollPane will provide scrollbars if there is not enough room.

How can I get the size of an applet's area, as defined in HTML?
Location: http://www.jguru.com/faq/view.jsp?EID=59925
Created: May 30, 2000 Modified: 2000-05-30 08:30:27.136
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Branislav Stofko (http://www.jguru.com/guru/viewbio.jsp?EID=59366

To get the applet's size, use the getWidth(), getHeight(), and getDimension() methods. The getWidth() and getHeight() methods were added with Java 1.2. Keep in mind an applet is just a glorified component.

I show a PopupMenu from a mouseEntered event. How can I close it on a mouseExited event?
Location: http://www.jguru.com/faq/view.jsp?EID=66153
Created: Jun 6, 2000 Modified: 2000-06-06 15:43:47.417
Author: Senthil D. Kumar (http://www.jguru.com/guru/viewbio.jsp?EID=16254) Question originally posed by John Twomey (http://www.jguru.com/guru/viewbio.jsp?EID=48460

In the mouseExited method you can do the following :

public void mouseExited(MouseEvent event)
{
      if ( _popupMenu.isVisible())
                _popupMenu.setVisible(false);
}

How can I show a modal dialog box from an Applet (in Internet Explorer)?
Location: http://www.jguru.com/faq/view.jsp?EID=67354
Created: Jun 7, 2000 Modified: 2000-09-14 08:30:33.177
Author: Krzysztof Raciniewski (http://www.jguru.com/guru/viewbio.jsp?EID=32358) Question originally posed by d sdvsd (http://www.jguru.com/guru/viewbio.jsp?EID=56415

There is article about this on the Microsoft web site (http://www.microsoft.com/java/sdk/40/kb/177753.htm) Remember that this works only on Internet Explorer and is not portable.

What is Java 2 AWT Native Interface (JAWT) and how can I use it for native rendering?
Location: http://www.jguru.com/faq/view.jsp?EID=66689
Created: Jun 7, 2000 Modified: 2000-06-07 10:18:23.536
Author: Davanum Srinivas (http://www.jguru.com/guru/viewbio.jsp?EID=2011)

There is an article at JavaWorld that explains this process:
http://www.javaworld.com/javaworld/javatips/f_jw-javatip86.html

How does one show a message in a popup-window from an applet?
Location: http://www.jguru.com/faq/view.jsp?EID=56939
Created: Jun 8, 2000 Modified: 2000-06-08 02:02:57.833
Author: Paolo Rocca (http://www.jguru.com/guru/viewbio.jsp?EID=56889) Question originally posed by Svend-Aage Nielsen (http://www.jguru.com/guru/viewbio.jsp?EID=53075

Just popup a Frame from your applet. This is your applet:

//File hello.java
import java.awt.*;
import java.applet.*;

public class hello extends Applet {
  Frame f = new helloFrame ();
  public void init() {
    setLayout (new FlowLayout());
    add (new Button("Click me"));
    /* this button allows you to pop up a frame */
  }
  public boolean action (Event evt, Object arg) {
    if (arg.equals("Click me")) {
      f.show();		// Show the popup window
      f.resize (150, 100);	// and resize it
      return true;
    }
    else return false;
  }
}

And this is your frame:

// File helloFrame.java
import java.awt.*;
import java.applet.*;

public class helloFrame extends Frame {
  public helloFrame() {
    setLayout (new FlowLayout());
    setTitle ("Hello!");			    // The window title
    add (new Label ("This is the message"));    // Your message
    add (new Button ("Ok"));		    // The button to quit
  }
  public boolean action (Event evt, Object arg) {
    if (arg.equals("Ok")) {
      dispose();
      return true;
    }
    else return false;
  }
}

You have to compile helloFrame first, and then you can compile hello. When you click on the button "click me" a popup window will be showed, with your message in it.

Can I use a mouse wheel with Swing controls?
Location: http://www.jguru.com/faq/view.jsp?EID=64267
Created: Jun 8, 2000 Modified: 2000-07-06 21:21:24.949
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Andreas Larsson (http://www.jguru.com/guru/viewbio.jsp?EID=49213

Java doesn't support this at this time. http://developer.java.sun.com/developer/bugParade/bugs/4289845.html shows it as an RFE, committed to the Merlin release, which I believe is 1.4.

If you don't care to wait for 1.4, see http://www.codeproject.com/java/mousewheel.asp for how to add it with the help of JNI.

How do i add support for Multiple Monitors in my Swing Application?
Location: http://www.jguru.com/faq/view.jsp?EID=70450
Created: Jun 9, 2000 Modified: 2000-06-09 10:56:56.289
Author: Davanum Srinivas (http://www.jguru.com/guru/viewbio.jsp?EID=2011)

Multiple monitor support has been added to JDK1.3:

http://java.sun.com/j2se/1.3/docs/guide/2d/new_features.html http://java.sun.com/j2se/1.3/docs/guide/2d/spec/j2d-awt.fm6.html#70485

How can I create internationalized accelerator keys (not mnemonics) for menu items? (The same menu item could have different accelerator keys for different languages.)
Location: http://www.jguru.com/faq/view.jsp?EID=61410
Created: Jun 9, 2000 Modified: 2000-06-09 11:08:11.346
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by Anil Punjabi (http://www.jguru.com/guru/viewbio.jsp?EID=23218

Use the following API

KeyStroke.getKeyStroke(String stringFormOfKeyStroke)

as in the following code:

public static KeyStroke getKeyStroke(String s)

Parse a string with the following syntax and return an a KeyStroke:

"<modifiers>* <key>"
modifiers := shift | control | meta | alt | button1 | button2 | button3
key := KeyEvent keycode name, i.e. the name following "VK_".

Here are some examples:

"INSERT" => new KeyStroke(0, KeyEvent.VK_INSERT);
"control DELETE" => new KeyStroke(InputEvent.CTRL_MASK, KeyEvent.VK_DELETE);
"alt shift X" => new KeyStroke(InputEvent.ALT_MASK | InputEvent.SHIFT_MASK, KeyEvent.VK_X);

Now, it becomes a matter of loading a locale based ResourceBundle which contains the map. For details on ResourceBundle please see the following URL -

http://java.sun.com/products/jdk/1.2/docs/api/java/util/ResourceBundle.html

To keep the uniqueness of the key is the responsibility of the person who localizes the resource bundle. You could write a GUI to wrap that functionality.

What audio file formats are supported with the Java 2 platform? Is there a difference between 1.2 and 1.3?
Location: http://www.jguru.com/faq/view.jsp?EID=72431
Created: Jun 25, 2000 Modified: 2000-06-25 09:18:12.09
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

According to http://java.sun.com/products/jdk/1.2/docs/guide/sound/index.html:

The following audio file formats are supported: AIFF, AU and WAV. In addition, the following MIDI-based song file formats are supported: MIDI TYPE 0, MIDI TYPE 1, and RMF.

The 1.3 documentation [http://java.sun.com/j2se/1.3/docs/guide/sound/index.html] do not seem to add more audio formats, just a software-based mixer and access to the MIDI hardware.

Prior to the Java 2 platform, for Java 1.0/1.1, only the AU format was supported.

How can i dynamically load fonts at runtime?
Location: http://www.jguru.com/faq/view.jsp?EID=74298
Created: Jun 25, 2000 Modified: 2000-06-25 09:21:44.883
Author: Davanum Srinivas (http://www.jguru.com/guru/viewbio.jsp?EID=2011)

Yes, This is possible in JDK1.3. The new method Font.createFont(int, InputStream) provides the ability to add fonts to the JVM at runtime. This font is not persistent upon termination of the JVM and is only available to the creator of the Font. At this time, only TrueTypeTM fonts can be created at runtime. The following code sample illustrates how to dynamically load the TrueType font Arial from a file:

File file = new File("Arial.ttf");
FileInputStream fis = new FileInputStream(file);
Font font = Font.createFont(Font.TRUETYPE_FONT, fis);	    

Similarly, to load the font from a URL:

URL url = new URL("Arial.ttf");
InputStream is = url.openStream();
Font font = Font.createFont(Font.TRUETYPE_FONT, is);

How do I use antialiasing in Java?
Location: http://www.jguru.com/faq/view.jsp?EID=79646
Created: Jun 25, 2000 Modified: 2000-07-01 22:20:13.837
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

In your paint() method, add the following hint at the top of the method:

((Graphics2D)g).setRenderingHint
  (RenderingHints.KEY_ANTIALIASING,
   RenderingHints.VALUE_ANTIALIAS_ON); 

[FAQ Manager Note] This will only work in Java2. In JDK 1.x, you cannot perform antialias automatically (you would have to write your own antialiasing routines)

What general techniques are in practice to generate Reports in java (both applets and applications)?
Location: http://www.jguru.com/faq/view.jsp?EID=79281
Created: Jun 25, 2000 Modified: 2000-07-28 12:55:02.957
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Chakree Chakree (http://www.jguru.com/guru/viewbio.jsp?EID=22927

In applets, its best to just generate another HTML page and use the printing capabilities of the browser. For applications, it is easiest to just acquire a reporting package already created, instead of trying to figure out the Java Printing API, dealing with pagination, etc. Some packages are:

• NetCharts
• ElixirReport
• PageLayout
• JReport
• RReport
• Style Report

How do I draw a line of any thickness in JDK 1.1?
Location: http://www.jguru.com/faq/view.jsp?EID=72470
Created: Jun 25, 2000 Modified: 2000-06-25 09:45:26.867
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Sergey Savenkov (http://www.jguru.com/guru/viewbio.jsp?EID=44661

Prior to the Java 2D API, all lines were drawn at a thinkness of one. If you need a wider line, you would need to draw multiple lines next to each other (or a rectangle, if the line is horizontal or veritcal - diagonal lines would need to be rotated if you relied on a filled rectangle)

How can I remove all the listeners associated with a component?
Location: http://www.jguru.com/faq/view.jsp?EID=72457
Created: Jun 25, 2000 Modified: 2000-06-25 10:01:04.902
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Zaneer Babu (http://www.jguru.com/guru/viewbio.jsp?EID=53849

Prior to 1.3, there was no way to ask a component for its list of listeners. You had to manually track them yourself. Starting with 1.3, you can ask certain AWT/Swing objects for said list of listeners, then remove them. Since Component has a getListeners(Class) method, all components have support this. See http://java.sun.com/j2se/1.3/docs/guide/swing/ListenerChanges.html for a list of non-component objects that support this.

[FAQ Manager Note] To remove all listeners prior to 1.3, you can simply create a new instance of the component in question and replace the old component with the new one.

Note that the getListeners() method will only work for the standard AWT events that Component tracks (and is overridden for each subclass). If you create your own subclass, you must override it to access any events that you add. See the source for java.awt.Button for an example of how to properly override getListeners().

Can I use a specifc font in a Swing application without asking the user of the application to alter the font.properties file?
Location: http://www.jguru.com/faq/view.jsp?EID=80405
Created: Jun 25, 2000 Modified: 2000-06-25 11:07:58.655
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by Indranil Dasgupta (http://www.jguru.com/guru/viewbio.jsp?EID=70647

The following resources may be helpful -

• http://java.sun.com/products/jdk/1.2/docs/guide/internat/physicalfont.html
• http://java.sun.com/products/jdk/1.2/docs/guide/internat/unicode_font.doc.html
• http://java.sun.com/products/jdk/1.2/docs/guide/internat/fontprop.html
• http://www.ibm.com/java/education/international-text/index.html

Jean-Baptiste Bugeaud adds...

You may use
Font.createfont(Font.TRUETYPE_FONT,this.getClass().getRessource("myfont.ttf"))

See http://java.sun.com/j2se/1.3/docs/api/java/awt/Font.html#createFont(int, java.io.InputStream) for details ...

Cool but only available in 1.3, and also works within applets!

Toolkit.getFontMetrics(Font) has been deprecated in Java 2. What do I use instead?
Location: http://www.jguru.com/faq/view.jsp?EID=72441
Created: Jun 25, 2000 Modified: 2000-06-25 11:09:40.665
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Kandula Radha (http://www.jguru.com/guru/viewbio.jsp?EID=70981

The java.awt.font.LineMetrics class provides the necessary information. Just ask the Font for the specific LineMetrics with getLineMetrics(). You'll need to know the string and the FontRenderContext, where the context is acquired from the Graphics2D object.

Font font = ...
FontRenderContext context = g2d.getFontRenderContext()
LineMetrics metrics = font.getLineMetrics("jGuru", context);

How can I create an application which contains multiple frames?
Location: http://www.jguru.com/faq/view.jsp?EID=88774
Created: Jun 29, 2000 Modified: 2000-06-29 15:26:57.161
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Upenra Modak (http://www.jguru.com/guru/viewbio.jsp?EID=45581

There is nothing special about having an application have multiple frames. Just create multiple Frame/JFrame objects. Each will share the same event thread so they cannot run completely independent of each other.

One thing worth mentioning is that often one doesn't create multiple frames, but instead uses one main Frame and subsequent frames are actually Dialog boxes. That way, if you were to iconify the Frame, the dialog boxes would be iconified automatically with them.

If you are looking more for an MDI-like architecture, consider using Swing's JDesktopPane with multiple JInternalFrame objects.

Is there anyway I can right-align text in a TextField?
Location: http://www.jguru.com/faq/view.jsp?EID=88926
Created: Jun 29, 2000 Modified: 2000-06-29 15:42:25.125
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Deepak Mahbubani (http://www.jguru.com/guru/viewbio.jsp?EID=53227

The AWT TextField doesn't support alignment. The Swing JTextField does. If you can, consider using it, instead.

jTextField.setHorizontalAlignment(JTextField.RIGHT);

Can I change the the mouse cursor to a different image when the mouse moves over a specific component in Java?
Location: http://www.jguru.com/faq/view.jsp?EID=88589
Created: Jun 29, 2000 Modified: 2000-06-29 15:43:35.03
Author: Simon Brown (http://www.jguru.com/guru/viewbio.jsp?EID=44588) Question originally posed by partha sarthi (http://www.jguru.com/guru/viewbio.jsp?EID=60808

All you need to do is add a mouse listener to your component and implement the mouseEntered and mouseExited methods to set and unset the cursor respectively. Here's an example :

myComponent.addMouseListener(new MouseAdapter() {
  public void mouseEntered(MouseEvent e) {
    myComponent.setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));
  }

  public void mouseExited(MouseEvent e) {
    myComponent.setCursor(Cursor.getDefaultCursor());
  }
});

How can I flash a minimized window to get the attraction of a user?
Location: http://www.jguru.com/faq/view.jsp?EID=88676
Created: Jun 29, 2000 Modified: 2000-06-29 15:52:12.536
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by Deepak Dureja (http://www.jguru.com/guru/viewbio.jsp?EID=62641

As long as the minimized window is still visible you could do -

try {
  for (int i = 0; i < 4; i++) {
      window.setVisible(false);
      window.setVisible(true);
  }
} finally {
  // leave it visible
  window.setVisible(true);
}

You are out of luck if your task autohide is "on" (MS windows only) or your minimized window is on a different virtual desktop.

What is the difference between hierarchical and delegate event handling in AWT?
Location: http://www.jguru.com/faq/view.jsp?EID=90530
Created: Jun 29, 2000 Modified: 2000-06-29 15:56:02.528
Author: RamaChandra Murthy (http://www.jguru.com/guru/viewbio.jsp?EID=74971) Question originally posed by Aniruddh Mishra (http://www.jguru.com/guru/viewbio.jsp?EID=36169

The hierarchical event handling in AWT specifies that the component interested in specific type of events has to handle events explicitly by the component i.e.,

1. By subclassing the component
2. By enabling the events in which the component is interested ini.e., by invoking enableEvents(long XXXevent)
3. By overriding the public void processXXXEvent(XXXEvent event) method.

This way of subclassing each component and enabling the events which the componet has to handle is a tedious and cumbersome process.Hence,generally the delegation model is preferred.

The delegation model specifies that each component can delegate the job of event handling to objects called Listeners which must register with the event source.. Whenever an event is fired from a component, an event object is propagated to an appropriate method in the Listener object, and that method contains code to handle the event. Corresponding to every AWTEvent there is a corresponding event listener. For example, for ActionEvent we have ActionListener.

How can I determine how many lines are in a TextArea or JTextArea?
Location: http://www.jguru.com/faq/view.jsp?EID=72674
Created: Jul 1, 2000 Modified: 2000-07-01 21:32:55.598
Author: Jan Borchers (http://www.jguru.com/guru/viewbio.jsp?EID=48743) Question originally posed by Grzegorz Kunstman (http://www.jguru.com/guru/viewbio.jsp?EID=69858

If you have a JTextArea with a PlainDocument (every child element represents a single ine) then you could do this:

Document doc = mytextarea.getDocument();
Element root = doc.getDefaultRootElement();
int lines = root.getElementCount();

Sandip Chitale adds

In both cases you could create a java.io.StringReader out of the getText() returned text. Wrap it in a java.io.BufferedReader and then read lines using the readLine() API.

You could walk through the String object returned by getText() and look for '\n' char to count the lines.

For JTextArea there is a direct API -

public int getLineCount();

John Zukowski adds

To manually count them:

String text = area.getText();
StringReader reader = new StringReader(text);
LineNumberReader lnr = new LineNumberReader(reader);
while (lnr.readLine() != null);
System.out.println(reader.getLineNumber());

Is there a way to know what percentage of a PrinterJob is currently complete. I would like to display a JProgressBar to show the percentage complete.
Location: http://www.jguru.com/faq/view.jsp?EID=93630
Created: Jul 2, 2000 Modified: 2000-07-02 15:35:59.975
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Steve O'Callaghan (http://www.jguru.com/guru/viewbio.jsp?EID=44533

There is no means to get this informatiom from standard Java. It might be possible with the help of JNI or Microsoft's J/Direct.

Why does the same text using the same font look different on different platforms? Is there any way to force it to look the same?
Location: http://www.jguru.com/faq/view.jsp?EID=93634
Created: Jul 2, 2000 Modified: 2000-07-02 15:39:50.103
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Kilian W (http://www.jguru.com/guru/viewbio.jsp?EID=59700

Fonts are dealt with in points from Java. How the Java runtime translates points to pixels is up to the implementor of the runtime. You have no control over this as a developer besides finding a point size that looks reasonably good on all the implementations you test with. Short of creating your own Java runtime implementation, and convincing people why it is required, you have no way to force the issue.

[FAQ Manager Note] If you always use layout managers to size and position your components in a GUI, it should never be necessary to worry about how text will look. Depending on the layout manager, you use, it can size the component based on its preferred size, which in turn is based on its font size and text to display.

See http://developer.java.sun.com/developer/onlineTraining/GUI/AWTLayoutMgr/index.html for details on layout management and which take preferred size into account.

Is it possible for a JWindow to stay on top of the Windows taskbar using Java code?
Location: http://www.jguru.com/faq/view.jsp?EID=93675
Created: Jul 2, 2000 Modified: 2000-07-02 17:09:40.382
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by garnet simpson (http://www.jguru.com/guru/viewbio.jsp?EID=67281

No. If the windows taskbar's 'always-on-top' property is set to true there is no way a pure Java JWindow can go on top of it.

What is GridBagLayout?
Location: http://www.jguru.com/faq/view.jsp?EID=96096
Created: Jul 5, 2000 Modified: 2000-07-05 05:59:30.024
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by priti shah (http://www.jguru.com/guru/viewbio.jsp?EID=95484

GridBagLayout is a standard layout manager provided with all Java implementations. Layout Managers help you to arrange Graphical User Interfaces that dynamically rearrange their components due to window size changes, as well as changes in fonts or other attributes of components such as displayed text.

You can find details about it at http://java.sun.com/docs/books/tutorial/uiswing/layout/gridbag.html

Note that GridBagLayout is extremely complex and should be avoided when possible. See my article, Effective Layout Management at http://developer.java.sun.com/developer/onlineTraining/GUI/AWTLayoutMgr/index.html for better ways to create layout managers through nesting simpler layouts. Nearly everything you can do in GridBagLayout can be done by nesting a few simpler layout managers.

Many people say "GridBagLayout isn't that bad -- I learned it". But they miss the point. One of the key issues in software development is that you should write your code so someone else can easily understand it. If you use GridBagLayout, anyone reading your code must know it at least as well as you to understand it. By sticking with simpler layout managers, the layout design is easier to "see" in the code.

How do I create scroll bars inside a dialog?
Location: http://www.jguru.com/faq/view.jsp?EID=96826
Created: Jul 5, 2000 Modified: 2000-07-08 08:05:42.879
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Amit Sharma (http://www.jguru.com/guru/viewbio.jsp?EID=89904

The Dialog component itself doesn't provide scrollbars. If you want to make them available, you have to place your set of components within a Container like a Panel, then place that container within a ScrollPane to provide the scrollbars.

Dialog dialog = new Dialog(mainFrame);
dialog.setLayout(new GridLayout(1,0));
    
Panel content = new Panel();
// set layout and add components for dialog to content panel

ScrollPane pane = 
    new ScrollPane(ScrollPane.SCROLLBARS_AS_NEEDED);
            
pane.add(content);
dialog.add(pane);

Note that if you are using Swing, you'll want to use JScrollPane instead of ScrollPane.

When is it recommended to use Java Advanced Imaging (JAI) instead of the Java 2D API?
Location: http://www.jguru.com/faq/view.jsp?EID=98328
Created: Jul 7, 2000 Modified: 2000-07-08 08:15:05.979
Author: Curtis Hatter (http://www.jguru.com/guru/viewbio.jsp?EID=62466) Question originally posed by Bruno Randolf (http://www.jguru.com/guru/viewbio.jsp?EID=94633

Basically it depends on the requirements of the program.

If I were able to do the required graphics with Java 2D, then I did so. But if I needed more advanced graphical capabilities then I would import the JAI package and convert my buffered image to a planar image and do what I needed.

For image loading I actually use Java Imaging I/O (since it will be part of 1.4 release) unless I need to read in images other then gif, jpg, or png.

Which brings me to another point.. if you wish to use images other than gif, jpg, or png, your only options (that I know of offered by SUN) are JIMI, and JAI. JAI offers a lot more then JIMI but does seem to use up a lot more memory and processing time. JIMI also is supposed to be jdk 1.1 compliant which could be a plus if you have to use a older jdk.

JAI also provides more information on the images then Java2D does, so if you need that info once again you might be better off with JAI.

How do I create my own events to pass between objects?
Location: http://www.jguru.com/faq/view.jsp?EID=98547
Created: Jul 8, 2000 Modified: 2000-07-08 17:51:44.77
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by Sivasankar Murugesan (http://www.jguru.com/guru/viewbio.jsp?EID=94465

Event firing in Java requires the following elements

• An event class to transmit information about the event
• An interface that describes how the bean will notify interested parties, known as listeners
• A data structure to track listeners
• Registration methods to add and remove listeners
• Code to fire the events

For example, suppose that you were creating a WeatherStation bean that notifies any interested parties when the sun rises or sets. This example is used throughout this FAQ.

An Event Class

The first requirement for event firing is a class to represent information about the event. The SunEvent object contains the time of the event and a boolean property that tells us if the event represents the sun rising or setting.

Event classes should be immutable. Immutable objects are ones that cannot be changed. Event firing passes a reference to a single event instance to each listener in an unspecified order. It is important that those listeners cannot modify the event, or it could change the way processing continues for other listeners. Note that the following class is not a bean, because its superclass does not implement java.io.Serializable. If you like, you can define the event object as a bean, but in practice this is rarely done.

Note that the event object must extend class java.util.EventObject. EventObject provides the getSource() method so you can determine the event origin. By extending EventObject, those objects can be handled generically in other methods, and some tools, like VisualAge for Java, take advantage of this when creating generic methods to forward events.

import java.util.Date;
import java.util.EventObject;

/**
 * An event that represents the Sun rising or setting
 */
public class SunEvent extends EventObject {
  private boolean risen;
  private Date date;
  
  public SunEvent(Object source, boolean risen, Date date) {
    super(source);
    this.risen = risen;
    this.date = date;
  }
  
  /** return a String representation of the date */
  public String getDate() {
    // return only a String representation
    //   so the user cannot modify the real date
    return date.toString();
  }
  
  /** return whether the sun rose or set */
  public boolean isRisen() {
    return risen;
  }
}

EventObject requires a source (a reference to the object that fired the event), which is set to the WeatherStation bean when firing the event. Whenever events are fired, an instance of the EventObject class is created and passed to each registered listener.

An Event-Listener Interface

Event listeners are classes that have registered interest in an event that a bean can fire. The bean notifies listener classes by calling certain methods in those listener classes. But how does the bean know which methods to call?

When defining the event, you also define a contract between the event source and its listeners. This contract specifies which methods the event source will call. Any listeners must implement those methods. Sounds like a perfect use for a Java language interface.

Therefore, define an interface that specifies the contract. Because each listener must implement that interface, the event-source bean can determine which methods it can call. Continuing the example, define a simple interface for the sun events.

Note that the following interface extends the java.util.EventListener interface. EventListener requires no methods. It is just a tag that indicates an interface is acting as an event listener. This assists determination of the events a bean can fire.

import java.util.EventListener;

/** A contract between a SunEvent source and
  *   listener classes
  */
public interface SunListener extends EventListener {
  /** Called whenever the sun changes position
    *   in a SunEvent source object 
    */
  public void sunMoved(SunEvent e);
}

Any SunEvent listeners are required to implement a single method, sunMoved(). Normally, event-listener methods should take a single parameter: the event object. However, if you have a strong need, the bean specification allows (but strongly discourages) different parameters.

An Event-Source Bean

Now you define the source of the sun events, the WeatherStation. This class needs to track its listeners and fire the events. This is implemented as follows, and a simple GUI to trigger the SunEvents is provided:

import java.util.Vector;
import java.util.Date;
import java.util.Enumeration;
import java.awt.Button;
import java.awt.Frame;
import java.awt.GridLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.Serializable;

/** A sample event source - this class fires SunEvents
  *   to anyone watching. A simple GUI is provided
  *   with "rise" and "set" buttons that cause the
  *   SunEvents to be fired.
  */
public class WeatherStation extends Frame 
                            implements Serializable {
  private transient Vector listeners;

  /** Provide a simple GUI that triggers our SunEvents
    */
  public WeatherStation() {
    super("Sun Watcher");
    setLayout(new GridLayout(1,0));
    Button riseButton = new Button("Rise");
    Button setButton = new Button("Set");
    add(riseButton);
    add(setButton);

    // make the "Rise" button fire "rise" SunEvents
    riseButton.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        fireSunMoved(true);
      }
    });

    // make the "Rise" button fire "set" SunEvents
    setButton.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        fireSunMoved(false);
      }
    });

    // Provide a means to close the application
    addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
        System.exit(0);
      }
    });
    
    pack();
  }

  /** Register a listener for SunEvents */
  synchronized public void addSunListener(SunListener l) {
    if (listeners == null)
      listeners = new Vector();
    listeners.addElement(l);
  }  

  /** Remove a listener for SunEvents */
  synchronized public void removeSunListener(SunListener l) {
    if (listeners == null)
      listeners = new Vector();
    listeners.removeElement(l);
  }

  /** Fire a SunEvent to all registered listeners */
  protected void fireSunMoved(boolean rose) {
    // if we have no listeners, do nothing...
    if (listeners != null && !listeners.isEmpty()) {
      // create the event object to send
      SunEvent event = 
        new SunEvent(this, rose, new Date());

      // make a copy of the listener list in case
      //   anyone adds/removes listeners
      Vector targets;
      synchronized (this) {
        targets = (Vector) listeners.clone();
      }

      // walk through the listener list and
      //   call the sunMoved method in each
      Enumeration e = targets.elements();
      while (e.hasMoreElements()) {
        SunListener l = (SunListener) e.nextElement();
        l.sunMoved(event);
      }
    }
  }
}

The bold text provides the support for tracking listeners and calling their event-handler methods.

The event source can now notify interested listeners. The synchronized keywords and cloning are necessary to avoid possible problems if the list of listeners changes while you are notifying listeners. Pressing the Rise and Set buttons fires an appropriate SunEvent to any registered listeners.

Typically, developers will create a fire method similar to the previous fireSunMoved() method, but the method is not required. The event-firing code can appear in any method you prefer.

A Sample Event Listener

In the example, the weather channel informs any interested parties about the sun rising or setting. Continuing this example, Mrs. Jones assigns her class the task of graphing the behavior of the sun. They must watch a weather channel to find out at exactly what time the sun rose and set each day, logging this information in their notebook. This example can be modeled using a Student class as follows:

/** A sample SunListener, logging when the sun rises and sets
  */
public class Student implements SunListener {
  private String name;

  /** constructor -- get the student's name */
  public Student(String name) {
    this.name = name;
  }

  /** sunMoved method comment. */
  public void sunMoved(SunEvent e) {
    log(name + "\tlogs : " +
        (e.isRisen() ? "rose" : "set") +
        " at " + e.getDate()); 
  }

  /** A simple log method - just print the text */
  protected void log(String text) {
    System.out.println(text);
  }
}

Note that Student implements SunListener, defining the details of a sunMoved() method. Any number of Students may watch the weather channel to hear the time of sunrise and sunset.

/**
 * A simple test of the SunEvent source and listeners
 */
public class WeatherTest {
  /** Run a test on the weather station, using Scott's
   *    kids as sample students
   */
  public static void main(String[] args) {
    // create a new sun event source
    WeatherStation w = new WeatherStation();

    // add some students to listen for sun rise/set
    w.addSunListener(new Student("Nicole"));
    w.addSunListener(new Student("Alex"));
    w.addSunListener(new Student("Trevor"));
    w.addSunListener(new Student("Claire"));

    // display the GUI for the weather channel
    w.setVisible(true);
  }
}

Running WeatherTest and pressing the Rise and Set buttons results in something like the following:

Nicole logs : rose at Thu Apr 29 14:55:21 PDT 1999
Alex   logs : rose at Thu Apr 29 14:55:21 PDT 1999
Trevor logs : rose at Thu Apr 29 14:55:21 PDT 1999
Claire logs : rose at Thu Apr 29 14:55:21 PDT 1999
Nicole logs : set at Thu Apr 29 14:55:22 PDT 1999
Alex   logs : set at Thu Apr 29 14:55:22 PDT 1999
Trevor logs : set at Thu Apr 29 14:55:22 PDT 1999
Claire logs : set at Thu Apr 29 14:55:22 PDT 1999

Warning

The above listener methods run in a specific order each time an event is fired. This is because we stored the listeners in an ordered data structure. There is no guarantee of event-notification order in the bean specification! Unless a bean documents its event-firing behavior as ordered, you should not assume any particular order of notification. Beans could store their listeners in any data, and they may report them in a different order every time they fire an event.

Also note that event firing is synchronous. That is to say, the event source calls only one event handler at a time. Most beans fire their events in this manner (although there is nothing to stop you from writing a bean that fires events asynchronously). Because of this, you should perform only short operations in your event handlers. Think of it this way: The next listener has to wait for you, so you should be courteous and return as quickly as possible. If you need more complex operations, spawn another thread from your event handler.

How do I scale, shear, translate, and/or rotate an image?
Location: http://www.jguru.com/faq/view.jsp?EID=98950
Created: Jul 9, 2000 Modified: 2000-07-11 17:17:20.488
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

Use the AffineTransform class, and pass it along to the drawImage() method.

• Create: AffineTransform trans = new AffineTransform()
• Scale: trans.scale(scalex, scaley)
• Shear: trans.shear(shiftx, shifty)
• Translate: trans.translate(deltax, deltay)
• Rotate: trans.rotate(radians)
• Draw: g2d.drawImage(image, trans, this)

How do I move the mouse cursor on the screen?
Location: http://www.jguru.com/faq/view.jsp?EID=98951
Created: Jul 9, 2000 Modified: 2000-07-11 17:22:35.055
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

Starting with 1.3 you can use the java.awt.Robot class:

Robot robot = new Robot();
robot.mouseMove(x, y);

Be sure your user is expecting this. Under normal circumstances, this should not be done.

How do I simulate keystrokes?
Location: http://www.jguru.com/faq/view.jsp?EID=98952
Created: Jul 9, 2000 Modified: 2000-07-11 17:25:02.632
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

Starting with 1.3 you can use the java.awt.Robot class:

Robot robot = new Robot();
robot.keyPress(KeyEvent.VK_J);
robot.keyRelease(KeyEvent.VK_J);

How do I simulate mouse events?
Location: http://www.jguru.com/faq/view.jsp?EID=98953
Created: Jul 9, 2000 Modified: 2000-07-11 17:27:35.114
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

Starting with 1.3 you can use the java.awt.Robot class:

Robot robot = new Robot();
robot.mousePress(InputEvent.BUTTON1_MASK);
robot.mouseRelease(InputEvent.BUTTON1_MASK);

How do I get the Shape from the outline of a text string?
Location: http://www.jguru.com/faq/view.jsp?EID=98976
Created: Jul 9, 2000 Modified: 2000-07-11 17:31:11.275
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

The getOutline() method of TextLayout provides this information:

TextLayout layout = new TextLayout(aString, aFont, g2d.getFontRenderContenxt());
// Argument is AffineTransform
Shape shape = layout.getOutline(null);

How do you convert a color image to a gray-scale image?
Location: http://www.jguru.com/faq/view.jsp?EID=99027
Created: Jul 9, 2000 Modified: 2000-07-11 17:36:23.549
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7)

Using the ColorSpace class, you can convert a multi-color image to gray with the following operation:

ColorSpace cs = ColorSpace.getInstance(ColorSpace.CS_GRAY);
ColorConvertOp op = new ColorConvertOp(cs, null);
BufferedImage grayImage = op.filter(colorImage, null);

How do you trap a newline/Enter character in a JTextArea?
Location: http://www.jguru.com/faq/view.jsp?EID=99650
Created: Jul 10, 2000 Modified: 2000-07-11 17:58:42.17
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by tanmay patil (http://www.jguru.com/guru/viewbio.jsp?EID=22776

There are multiple ways -

• 
  jtextArea.getDocument().addDocumentListener(
    new DocumentListener() {
      public void insertUpdate(DocumentEvent e) {
        // watch for newline/enter here
      }
      public void removeUpdate(DocumentEvent e) {
      }
      public void changedUpdate(DocumentEvent e) {
        // watch for newline/enter here
      }
  
    }
  }
  

• Add a KeyListener and look for VK_ENTER key typed event.

• 
  jtextArea.registerKeyboardAction(
    KeyStroke.getKeyStroke(VK_ENTER, 0, false),
    new ActionListener() {...}
  );
  

How can I load an image into a BufferedImage without creating a Component for the MediaTracker?
Location: http://www.jguru.com/faq/view.jsp?EID=99988
Created: Jul 11, 2000 Modified: 2000-07-11 18:02:14.539
Author: Bruno Randolf (http://www.jguru.com/guru/viewbio.jsp?EID=94633) Question originally posed by Bruno Randolf (http://www.jguru.com/guru/viewbio.jsp?EID=94633

You can achieve this by using an ImageIcon:

private BufferedImage loadBufferedImageIcon( String filename )
{
  // Get Image
  ImageIcon icon = new ImageIcon(filename);
  Image image = icon.getImage();

  // Create empty BufferedImage, sized to Image
  BufferedImage buffImage = 
    new BufferedImage(
    image.getWidth(null), 
    image.getHeight(null), 
    BufferedImage.TYPE_INT_RGB);
	
  // Draw Image into BufferedImage
  Graphics g = buffImage.getGraphics();
  g.drawImage(image, 0, 0, null);

  return buffImage;
}

How can I specify the initial position and size of a Frame/JFrame?
Location: http://www.jguru.com/faq/view.jsp?EID=100082
Created: Jul 11, 2000 Modified: 2000-07-11 18:12:22.061
Author: Simon Brown (http://www.jguru.com/guru/viewbio.jsp?EID=44588) Question originally posed by Yogesh Gupta (http://www.jguru.com/guru/viewbio.jsp?EID=55604

To set the size on a frame (or JFrame), use the setSize() method, passing either a Dimension object, or the width and height values in pixels. For example :

myFrame.setSize(640, 480);

Another (and IMHO better) way of sizing a window is to use the pack() method. This sizes the window so that each of its components are visible at their preferred size.

To set the initial position for a frame (or JFrame), use the setLocation() method specifying a Point object, or the x and y coordinates. The top-left of the screen is at 0,0.

myFrame.setLocation(0, 0);

These along with other useful methods are defined on java.awt.Component class.

The java.awt.Toolkit class contains the getScreenSize() method for getting the size of the screen - just in case you wish to make the window the full size of the screen or center your window.

What support exists in Java for a Multi-Screen Environment?
Location: http://www.jguru.com/faq/view.jsp?EID=100694
Created: Jul 12, 2000 Modified: 2000-07-19 16:40:13.751
Author: Davanum Srinivas (http://www.jguru.com/guru/viewbio.jsp?EID=2011)

You can now render on multiple screens by creating Frame, JFrame, Window, or JWindow objects with the GraphicsConfiguration of a target GraphicsDevice. For more information look at http://java.sun.com/j2se/1.3/docs/guide/2d/spec/j2d-awt.fm6.html

What are the advantages/disadvantages of Swing over AWT?
Location: http://www.jguru.com/faq/view.jsp?EID=106026
Created: Jul 19, 2000 Modified: 2000-07-19 16:59:45.417
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by namit gautam (http://www.jguru.com/guru/viewbio.jsp?EID=96784

Swing provides a richer set of components than AWT. They are 100% Java-based.

AWT on the other hand was developed with the mind set that if a component or capability of a component wasn't available on one platform, it won't be available on any platform. Something quickly portable from platform x, to y, to z. Due to the peer-based nature of AWT, what might work on one implementation might not work on another, as the peer-integration might not be as robust. Many of the original AWT problems were traceable to differences in peer implementations.

This is not to say that there are less bugs in Swing, though most are out these days. Its just that if a bug exists in Swing, its the same problem on all platforms, which was not the case with AWT.

[FAQ Manager Note] There are a few other advantages to Swing over AWT:

• Swing provides both additional components and added functionality to AWT-replacement components
• Swing components can change their appearance based on the current "look and feel" library that's being used. You can use the same look and feel as the platform you're on, or use a different look and feel
• Swing components follow the Model-View-Controller paradigm (MVC), and thus can provide a much more flexible UI.
• Swing provides "extras" for components, such as:
  • Icons on many components
  • Decorative borders for components
  • Tooltips for components
• Swing components are lightweight (less resource intensive than AWT)
• Swing provides built-in double buffering
• Swing provides paint debugging support for when you build your own components

Swing also has a few disadvantages:

• It requires Java 2 or a separate JAR file
• If you're not very careful when programming, it can be slower than AWT (all components are drawn)
• Swing components that look like native components might not act exactly like native components

How can I create multiple floatable/dockable toolbars/palettes/views which stay inside the application frame (unlike Swing JToolBars)? Is it poosible to have such a framework for AWT also?
Location: http://www.jguru.com/faq/view.jsp?EID=107014
Created: Jul 20, 2000 Modified: 2000-07-20 18:35:23.076
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Sandip Chitale PREMIUM (http://www.jguru.com/guru/viewbio.jsp?EID=14537

To keep toolbars within the application frame, you'll need to create your own JToolBar-like component that keeps the floating toolbar within a JInternalFrame instead of a JFrame. The UI for the JToolBar class requires that the floating frame be a JFrame: protected JFrame createFloatingFrame(JToolBar toolbar) and the drag window be a DragWindow (which extends Window).

As far as dealing multiple toolbars goes, if you want to stick with JToolBar... You will need to create a new ToolBarUI and override public void setFloating(boolean b, Point p), protected void dragTo(Point position, Point origin), and protected void floatAt(Point position, Point origin) to deal with adding multiple toolbars to a single constraint.

What is the difference between a JavaBean and a traditional AWT object?
Location: http://www.jguru.com/faq/view.jsp?EID=107018
Created: Jul 20, 2000 Modified: 2000-07-20 18:37:13.034
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Dallas Dreyer (http://www.jguru.com/guru/viewbio.jsp?EID=58484

JavaBeans is a component architecture for defining reusable components for Java. The JavaBeans specification defines just how to create/define such components. These components may be graphical or may not be. There is no requirement that a bean be graphical, just that it follows the architecture defined by the specification.

On the other hand, an AWT object, specifically the AWT components, are JavaBean components specifically designed to be reused by a drag-and-drop GUI development tool like VisualAge for Java or JBuilder. While yes, you can code everything by hand, because the AWT components are JavaBean components, you can get/set bean properties, connect events, and persist the interface, through the JavaBeans architecture.

How can I scroll the TextArea from an independent scrollbar in the same manner as its own scrollbar would scroll it?
Location: http://www.jguru.com/faq/view.jsp?EID=107019
Created: Jul 20, 2000 Modified: 2000-07-20 18:42:28.246
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by sudhakar chintu (http://www.jguru.com/guru/viewbio.jsp?EID=78272

The TextArea component does not expose this, as the scrollbar is part of the native component.

If you can, consider using the JTextArea component which exposes this, allowing you to share the model between the JScrollBar of the JScrollPane that the JTextArea is within and your external JScrollBar.

Is it possible to use AWT layout managers with Swing components?
Location: http://www.jguru.com/faq/view.jsp?EID=107138
Created: Jul 20, 2000 Modified: 2000-07-20 19:20:18.302
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by Nripesh Palikhya (http://www.jguru.com/guru/viewbio.jsp?EID=99684

But of course!

Sometimes people have the impression that you can only use Swing or only use AWT. This is not the case.

Swing builds on top of AWT's Container class, and uses the same layout managers and much of the other component support that AWT does.

To use the AWT layout managers with a Swing GUI, simply include

import java.awt.*;

at the top of your source, as well as the Swing package imports that you need. You will then be able to access all of the AWT layout managers.

BTW: You can also use Swing's BoxLayout layout manager in AWT-only applications -- it's just a standard layout manager. Make sure you deliver the BoxLayout class, as well as the SizeRequirements class from Swing with your AWT application if you do this.

When I change GUI (add/remove components) in an actionPerformed method, how can I force it update immediately? Calling revalidate seems delay the update until method actionPerformed returns.
Location: http://www.jguru.com/faq/view.jsp?EID=107177
Created: Jul 20, 2000 Modified: 2000-07-20 19:44:22.855
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by Chuong Huynh (http://www.jguru.com/guru/viewbio.jsp?EID=77266

The actionPerformed method is being called by the AWT thread.

The AWT thread is the thread that actually performs the repaint/revalidate request. Because that thread is tied up processing actionPerformed, it cannot do the update.

The only way you can do this (assuming you're doing some processing that takes a bit of time) is to start another thread for the processing. Note that if this other thread wants to update the GUI components, it should use Swing's invokeLater functionality to schedule the GUI update with the AWT thread. For example:

public void actionPerformed(ActionEvent e) {
  new Thread() {
    public void run() {
      doSomething();
      // update GUI
      SwingUtilities.invokeLater(new Runnable() {
        public void run() {
          fooLabel.setText("working...");
        }});
    }
  }.start();
}

(Sorry about the nested anon inner classes, but hopefully you'll get the point.)

Starting a thread to do a long-running action inside the actionPerformed method frees the AWT thread to actually update the GUI when you want it to

Can I change the look and feel of AWT components as can be done for Swing?
Location: http://www.jguru.com/faq/view.jsp?EID=107251
Created: Jul 20, 2000 Modified: 2000-07-20 20:28:38.696
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by shiva prasad (http://www.jguru.com/guru/viewbio.jsp?EID=73834

No. AWT components use native GUI widgets on each platform. They will always look like the current platform's look and feel.

How can I create a Java Image out of an integer array that I got from native code (using JNI)?.
Location: http://www.jguru.com/faq/view.jsp?EID=107797
Created: Jul 21, 2000 Modified: 2000-07-21 09:23:52.694
Author: Davanum Srinivas (http://www.jguru.com/guru/viewbio.jsp?EID=2011) Question originally posed by gv lakshmanan (http://www.jguru.com/guru/viewbio.jsp?EID=100651

You can create an ImageIcon from a Byte Array. So all you have to do is get the Byte Array from using JNI and create an ImageIcon from it. Here's how the code looks on the java side.

import javax.swing.*;

public class MyImage 
{ 
 static { System.loadLibrary("imagelib"); }
 ImageIcon getImage()
 {
   return new ImageIcon(getMyImage());
 }
 static native byte [] getMyImage(); 
}  

and here's the native code

JNIEXPORT jbyteArray JNICALL Java_MyImage_getMyImage (JNIEnv *env, jclass jC) 
{ 
 jbyte *buf ; 
 jsize size ;
 jbyteArray jb;

 // fill the buf
 buf  = ....
 size = ....

 // create the byte array
 jb=(*env)->NewByteArray(env, size);

 // fill the byte array
 (*env)->SetByteArrayRegion(env, jb, 0, size, buf);
 return jb;
}

How can I display tif graphics in my Java applet?
Location: http://www.jguru.com/faq/view.jsp?EID=107798
Created: Jul 21, 2000 Modified: 2000-09-14 08:37:36.111
Author: delfim martins (http://www.jguru.com/guru/viewbio.jsp?EID=9614) Question originally posed by Yasar Qureshi (http://www.jguru.com/guru/viewbio.jsp?EID=48204

A few options to solve this problem

• JIMI (Java Image Mangagement Interface) at http://java.sun.com/products/jimi
• JAI (Java Advanced Imaging) at http://java.sun.com/products/java-media/jai
• Lizard's TIFF Library at http://www.lizardworks.com/java.html

It is up to you which one to choose. They are all very good.

How can I save a JApplet's output (AppletWindow) as a GIF file?
Location: http://www.jguru.com/faq/view.jsp?EID=108121
Created: Jul 21, 2000 Modified: 2000-09-14 08:38:00.007
Author: Joe Hanink (http://www.jguru.com/guru/viewbio.jsp?EID=94909) Question originally posed by karuppanan rameshkumar (http://www.jguru.com/guru/viewbio.jsp?EID=102591

Visit http://www.acme.com/java/software/Acme.JPM.Encoders.GifEncoder.html for a prebuilt utility

On my win2k system, a call to System.getProperty("awt.toolkit") returns a value of "sun.awt.windows.WToolkit". Where exactly is the "sun.awt.windows.WToolkit" value coming from?
Location: http://www.jguru.com/faq/view.jsp?EID=109481
Created: Jul 24, 2000 Modified: 2000-07-29 20:50:02.911
Author: Davanum Srinivas (http://www.jguru.com/guru/viewbio.jsp?EID=2011) Question originally posed by Doug Dew (http://www.jguru.com/guru/viewbio.jsp?EID=28727

The System property "awt.toolkit" is used to load alternative Toolkit's if needed. See http://java.sun.com/j2se/1.3/docs/api/java/awt/Toolkit.html for more info.

The default value that you get is used and set by Sun's implementation of JDK. If you use microsoft's JVM then you will get "com.ms.awt.WToolkit" instead.

How can I write from right to left (e.g. hebrew) in a TextField/TextArea?
Location: http://www.jguru.com/faq/view.jsp?EID=109545
Created: Jul 24, 2000 Modified: 2000-07-29 20:23:57.832
Author: Kaloian Doganov (http://www.jguru.com/guru/viewbio.jsp?EID=109010) Question originally posed by ronen portnoy (http://www.jguru.com/guru/viewbio.jsp?EID=27420

Use ComponentOrientation property of almost all Swing components. Here is an example with JTextArea and Hebrew:

Locale hebrew = new Locale("he", "IL");
JTextArea area = new JTextArea();
area.setComponentOrientation(ComponentOrientation.getOrientation(hebrew));

With about 8% of men and 0.5% of women color-blind, what should I take into consideration when designing a GUI?
Location: http://www.jguru.com/faq/view.jsp?EID=109794
Created: Jul 24, 2000 Modified: 2000-07-29 05:58:43.882
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by John Zukowski PREMIUM (http://www.jguru.com/guru/viewbio.jsp?EID=7

I do not know if the factoid about Men and Women matters :)

Well, the simple thing that comes to my mind is that you should not use only Color to encode a piece of information. A very good example is MS Word. It uses green colored wavy underline to show grammatical mistakes and red colored wavy underline to show spelling mistakes.

Having said that, in the real world the traffic signal systems in most contries use the red and green colors which reportedly are the one most confusing to the color-blind.

Second thing is that the application should try to honour the users desktop color setting. That goes for normal display as well as selection highlight and other highlight etc. User may have set a color scheme to what may seem wierd to you because of their color blindness...

How can I display Help from a dialog box when the corresponding Help button is clicked?
Location: http://www.jguru.com/faq/view.jsp?EID=111805
Created: Jul 26, 2000 Modified: 2000-07-29 20:32:13.782
Author: Sandip Chitale (http://www.jguru.com/guru/viewbio.jsp?EID=14537) Question originally posed by Tina Balla (http://www.jguru.com/guru/viewbio.jsp?EID=62523

Add a JButton("Help") to the dialog. Add java.awt.event.ActionListener implementation to it using the button.addActionListener(...);. Then in the actionPerformed(...) callback you could show the help. The choices are -

• Show the help in another java.awt.Frame. This may run into problems if your Dialog was "modal" (this is because the "modality" has been shifting it's meaning from version to version of Java).
• Show it in another non-modal dialog
• Run an external help program e.g.
  • WinHelp.exe
  • Browser
  Using the Runtime.exec("external command");

How can I draw a dotted line in AWT?
Location: http://www.jguru.com/faq/view.jsp?EID=114099
Created: Jul 29, 2000 Modified: 2000-07-29 20:22:52.072
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by ramesh vojjala (http://www.jguru.com/guru/viewbio.jsp?EID=103376

Prior to introducing the Java 2D API into the Java 2 platform, all lines drawn were a single pixel wide solid lines of a single color. So, if you wanted a dotted line in 1.0 or 1.1, you had to do all the intermediate drawing steps yourself.

With the Java 2D API though, you can define a Stroke to define the drawing pen. For dotted lines, you would need to use the BasicStroke constructor that accepted six arguments:

public BasicStroke
  (float width,
   int cap,
   int join,
   float miterlimit,
   float[] dash,
   float dash_phase)

So, for a dotted line, an example might look like:

import java.awt.*;
import java.awt.geom.*;
import java.applet.*;

public class Stroked extends Applet {
  public void paint (Graphics g) {
    Graphics2D g2d = (Graphics2D)g;

    Rectangle2D rectangle = 
      new Rectangle2D.Double (
      20, 20, 200, 100);
    g2d.setColor (Color.blue);
    g2d.setStroke (new BasicStroke(
      1f, 
      BasicStroke.CAP_ROUND, 
      BasicStroke.JOIN_ROUND, 
      1f, 
      new float[] {2f}, 
      0f));
    g2d.draw (rectangle);
  }
}

Using Java Layout Managers, can a Container be added to another Container?
Location: http://www.jguru.com/faq/view.jsp?EID=114263
Created: Jul 29, 2000 Modified: 2000-07-29 21:08:32.67
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by Khaja Hussain Muchumarri (http://www.jguru.com/guru/viewbio.jsp?EID=94096

But of course!

Container is a subclass of Component, and because any Component can be added to a Container, Containers can be added to other containers.

Please see http://developer.java.sun.com/developer/onlineTraining/GUI/AWTLayoutMgr for details on how you nest Containers like this to create useful layouts.

How do I convert an image from RenderedImage to BufferedImage?
Location: http://www.jguru.com/faq/view.jsp?EID=114602
Created: Jul 30, 2000 Modified: 2000-08-01 15:52:28.889
Author: clemens privacy (http://www.jguru.com/guru/viewbio.jsp?EID=114598) Question originally posed by delfim martins (http://www.jguru.com/guru/viewbio.jsp?EID=9614

There doesn't seem to be a direct way to do it, but try the following:

BufferedImage mine = 
    new BufferedImage(renderimage.getWidth(),
                      renderimage.getHeight(),
                      BufferedImage.TYPE_INT_RBG);
mine.getGraphics().drawImage(renderimage,0,0,NULL);

How can I implement a password field like JPasswordField with AWT?
Location: http://www.jguru.com/faq/view.jsp?EID=115225
Created: Jul 31, 2000 Modified: 2000-08-01 15:54:54.578
Author: Davanum Srinivas (http://www.jguru.com/guru/viewbio.jsp?EID=2011) Question originally posed by Mehmet Ali OK (http://www.jguru.com/guru/viewbio.jsp?EID=55329

java.awt.TextField has a setEchoChar which can be used to implement a password field. Here's some sample code.

import java.awt.*;
import java.awt.event.*;

public class PasswordDemo extends Frame {
    public PasswordDemo() {
        TextField password = new TextField(10);
        password.setEchoChar('*');
        add(password);
    }
    public static void main(String[] argv) {
        final PasswordDemo f = new PasswordDemo();
        f.pack();
        f.setVisible(true);
        f.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
    }
}

How can I determine which card is curently being displayed in a CardLayout?
Location: http://www.jguru.com/faq/view.jsp?EID=116482
Created: Aug 1, 2000 Modified: 2000-08-01 16:25:55.332
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by ar_vin rupak (http://www.jguru.com/guru/viewbio.jsp?EID=109932

The displayed component will be the only one in the container that is visible.

You can walk through the components in the container and check which one is visible.

For example, to determine if you're on the first or last component (perhaps to disable "previous" and "next" buttons) you could do something like the following (assuming p is the panel with the CardLayout)

boolean firstShowing = 
  p.getComponent(0).isVisible();

boolean lastShowing = 
  p.getComponent(p.getComponentCount()-1).isVisible();

What image file formats can (Applet and Tookit).getImage() use?
Location: http://www.jguru.com/faq/view.jsp?EID=118670
Created: Aug 3, 2000 Modified: 2000-08-03 17:50:04.064
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Carfield Yim (http://www.jguru.com/guru/viewbio.jsp?EID=4648

The GIF and JPEG formats have been accepted since the beginning of Java time. The XBM format has been accepted since Java 1.0 also, but is not widely mentioned as it isn't a popular format. Starting with the 1.3 release, PNG support is now standard, too.

How can I render a screen containing Graphics objects like rectangle, lines, texts etc into PostScript?
Location: http://www.jguru.com/faq/view.jsp?EID=118857
Created: Aug 3, 2000 Modified: 2000-08-04 19:34:50.733
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Saptadeep Dutta (http://www.jguru.com/guru/viewbio.jsp?EID=33770

The easiest way is to install a Postscript printer driver to your native OS, use the standard Java printing API and print to a file, selecting the newly installed printer in the process.

Is there a way to send Windows-specific messages from Java to IE or Netscape without using the ms package? (i.e. WM_CLOSE, WM_MOUSEEVENT...)
Location: http://www.jguru.com/faq/view.jsp?EID=118861
Created: Aug 3, 2000 Modified: 2000-08-04 19:51:43.293
Author: John Zukowski (http://www.jguru.com/guru/viewbio.jsp?EID=7) Question originally posed by Tre Guru (http://www.jguru.com/guru/viewbio.jsp?EID=98227

You can write JNI code that does the equivalent of the ms.* packages. There is no native support in Java to do this though (hence Microsoft providing this in their ms.* package).

Is it possible to change the shape of a JButton/Button to be triangular?
Location: http://www.jguru.com/faq/view.jsp?EID=119370
Created: Aug 4, 2000 Modified: 2000-08-04 19:37:26.257
Author: Davanum Srinivas (http://www.jguru.com/guru/viewbio.jsp?EID=2011) Question originally posed by Jenny Yang (http://www.jguru.com/guru/viewbio.jsp?EID=116713

Here's a sample based on JDC Tech Tips, August 26, 1999

import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;

public class TriangleButton extends JButton {
  public TriangleButton(String label) {
    super(label);

    // These statements enlarge the button so that it 
    // becomes a circle rather than an oval.
    Dimension size = getPreferredSize();
    size.width = size.height = Math.max(size.width, 
      size.height);
    setPreferredSize(size);

    // This call causes the JButton not to paint 
    // the background.
    // This allows us to paint a round background.
    setContentAreaFilled(false);
  }

  // Paint the round background and label.
  protected void paintComponent(Graphics g) {
    if (getModel().isArmed()) {
      // You might want to make the highlight color 
      // a property of the RoundButton class.
      g.setColor(Color.lightGray);
    } else {
      g.setColor(getBackground());
    }
    
    int x3Points[] = {getSize().width/2, 0, getSize().width};
    int y3Points[] = {0, getSize().height, getSize().height};
    g.fillPolygon(x3Points, y3Points, x3Points.length); 

    // This call will paint the label and the 
    // focus rectangle.
    super.paintComponent(g);
  }

  // Paint the border of the button using a simple stroke.
  protected void paintBorder(Graphics g) {
    g.setColor(getForeground());
    int x3Points[] = {getSize().width/2, 0, getSize().width};
    int y3Points[] = {0, getSize().height, getSize().height};
    g.drawPolygon(x3Points, y3Points, x3Points.length); 
  }

  // Hit detection.
  Polygon polygon;
  public boolean contains(int x, int y) {
    // If the button has changed size, 
    // make a new shape object.
    if (polygon == null || 
      !polygon.getBounds().equals(getBounds())) {
      int x3Points[] = {getSize().width/2, 0, getSize().width};
      int y3Points[] = {0, getSize().height, getSize().height};
      polygon = new Polygon(x3Points,y3Points,3);
    }
    return polygon.contains(x, y);
  }

  // Test routine.
  public static void main(String[] args) {
    // Create a button with the label "Jackpot".
    JButton button = new TriangleButton("Jackpot");
    button.setBackground(Color.green);

    // Create a frame in which to show the button.
    JFrame frame = new JFrame();
    frame.getContentPane().setBackground(Color.yellow);
    frame.getContentPane().add(button);
    frame.getContentPane().setLayout(new FlowLayout());
    frame.setSize(150, 150);
    frame.setVisible(true);
  }
}

Is there any way to generate offscreen images without relying on the native graphics support? I'd like to create an image without an X server running, or create an image with more colors than the current video mode.
Location: http://www.jguru.com/faq/view.jsp?EID=121936
Created: Aug 8, 2000 Modified: 2000-09-18 09:31:11.489
Author: Scott Stanchfield (http://www.jguru.com/guru/viewbio.jsp?EID=11) Question originally posed by David Noel (http://www.jguru.com/guru/viewbio.jsp?EID=119574

You must have a graphical environment installed on your server to work with Java image routines in AWT, even though the image will only be displayed on the client's machine.

The AWT image manipulation routines use the native platform's graphics primitives and "grab" the resulting image to send to the client.

How do I store anti-aliased images as GIF files while preserving all used colors (like Photoshop does)?
Location: http://www.jguru.com/faq/view.jsp?EID=122164
Created: Aug 8, 2000 Modified: 2000-08-13 18:04:44.659
Author: Rob Edmondson (http://www.jguru.com/guru/viewbio.jsp?EID=35309) Question originally posed by Mathias Bogaert (http://www.jguru.com/guru/viewbio.jsp?EID=119306

A gif file supports a maximum of 256 colours. However, the palette entries are 888RGB (24 bit) format. If you use efficient filters and colour reduction with the original image before converting to gif, you should get better results. If you need better image quality, use JPEG and low (or no) image compression.

Where can I get Java source for drawing 3D graphs?
Location: http://www.jguru.com/faq/view.jsp?EID=124573
Created: Aug 10, 2000 Modified: 2000-08-13 18:01:24.331
Author: Venkatesan R (http://www.jguru.com/guru/viewbio.jsp?EID=124537) Question originally posed by Paresh Rana (http://www.jguru.com/guru/viewbio.jsp?EID=114277

You can get 3d animations, graphs from many sites like:

• http://www.javafile.com
• http://www.javaboutique.com
• http://www.planet-source-code.com
• http://www.codeguru.com

And many more...

Is it possible to make the background of a Label (not JLabel) transparent?
Location: http://www.jguru.com/faq/view.jsp?EID=126754
Created: Aug 14, 2000 Modified: 2000-08-14 20:53:29.373
Author: John Zukowski (ht