Collections Section Index | Page 7

In order to get all the keys for a Hashtable, you use the keys() method to get an Enumeration or the keySet() method to get a Set. If you are using Java 2, and can use the collections framework, w...more

The Collections class has six methods to help out here: unmodifiableCollection(Collection c) unmodifiableList(List list) unmodifiableMap(Map m) unmodifiableSet(Set s) unmodifiableSortedMap(Sorted...more

To go through all the elements of a HashMap, or any class that implements the Map interface, call the entrySet() or keySet() methods than loop through what is returned. The entrySet() returns a gr...more

The Hashtable class uses an internal (private) class named Entry to hold the key-value pairs. All entries of the Hashtable are stored in an array of Entry objects with the hash value of the key se...more

If speed is of the essence, do not use a Vector. Instead, use an ArrayList. All accesses to a Vector are synchronized, whether you need it or not. If you know you aren’t accessing the structu...more

You can wait for Generics to be added to Java or... You'd have to build one yourself. Basically, you're creating a class that is a Proxy (Gang Of Four design pattern) around the actual Collectio...more

With Collections by themselves, there isn't one. What you're asking for is a Labeled Directed Graph (A directed graph where the graph edges have labels describing the relationship). A rather com...more

You can use Java property files for storing settings for an application. Use the java.util.Properties class, which includes a load and store method. You can also use a PropertyResourceBundle, but ...more

You can't. Each of the Map and List interfaces define a remove(Object o) method. Each method returns a different type (Map returns an Object while List returns a boolean). Because the compiler doe...more

The Arrays class in java.util provides a series of sort() methods for sorting arrays. If the array is an array of primitives or an array of a class that implements Comparable then you can just cal...more

The System.getProperties() method will return the standard property set. However, in untrusted applets, you can only ask for specific properties, as in System.getProperty("java.version").more

You cannot. It is part of the security architecture of the Java runtime to ensure never accessing invalid memory space.

If you have an array of primitives or an array of equivalent objects that implement the Comparable interface, all you need to do is call the sort() method of the java.util.Arrays class. If the cla...more

To avoid getting an ArrayIndexOutOfBoundsException, you can check for the array length from either the length instance variable or using reflection and calling java.lang.reflect.Array.getLength(),...more

With the Collections Framework, the new implementations are all unsynchronized by default. If you need synchronized access, you must synchronize things yourself. The Collections class offers a wra...more