focusdemo.java

这是清华大学编写的JAVA教材中所有题目的源代码！

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

class FocusDemo  
{
	Frame f=new Frame("焦点示例");
	TextField tf1=new TextField(20);
	TextField tf2=new TextField(20);
	Button btn1=new Button("button1");
	Button btn2=new Button("button2");
	
	public FocusDemo() 
	{
		f.addWindowListener(new WindowAdapter()
		{
			public void windowClosing(WindowEvent e)
			{
				System.exit(0);
			}
		});
		
		tf1.addFocusListener(new FocusAdapter()
		{
			public void focusLost(FocusEvent f)
			{
				String s=tf1.getText();
				if(s.length()!=6)
				{
					tf2.setText("请输入6个字符");
					tf1.setText("");
					tf1.requestFocus();
				}
				else
				{
					tf1.transferFocus();
				}
			}
		});

		btn1.setFocusable(false);
		
		f.add(tf1,BorderLayout.NORTH);
		f.add(tf2,BorderLayout.SOUTH);
		f.add(btn1,BorderLayout.WEST);
		f.add(btn2,BorderLayout.EAST);
		f.setSize(300,100);
		f.setVisible(true);		
	}
	
	public static void main(String args[])
	{
		new FocusDemo();
	}
}