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

class TestFrame extends Frame {
    private TextField tf;
    private Button bt;
    public TestFrame() {
        setSize(200,80);
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        }); 
        add(tf=new TextField("blank"),BorderLayout.NORTH);//These are points for your question
        add(bt=new Button("Button"),BorderLayout.SOUTH);//
        bt.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                tf.setText("TextField");
            }
        });
    }
}
public class TestAWT {
    public static void main(String[] args) {
        Frame w=new TestFrame();
        w.setVisible(true);
    }
}