本题的功能是定义图形按钮。窗口中有两个图形按钮，当鼠标移上去时，图形按钮的图形将改变，用鼠标单击按钮时图形按钮的图形又发生改变，当鼠标左键松开或者移开鼠标后，图形按钮的图形又恢复原样。
import javax.swing.*;
import java.awt.*;
public class java3 extend JButton
public java3(Icon icon,Icon pressed,Icon rollover)
this(icon);
setFocusPainted(false);
setRolloverEnabled(true);
setRolloverIcon(rollover);
setPressedIcon(pressed);
setBorderPainted(false);
setContentAreaFilled(false);
public static void main(String[]args)
java3 b1=new java3(
new ImageIcon("java3-redcube.gif"),
new ImageIcon("java3-redpaw.gif"),
new ImageIcon("java3-reddiamond.gif"));
java3 b2=new java3(
new ImageIcon("java3-bluecube.gif"),
new ImageIcon("java3-bluepaw.gif"),
new ImageIcon("java3-bluediamond.gif"));
JFrame f=new JFrame();
f.setTitle("java3");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
c=f.getContentpane();
c.setLayout(new FlowLayout());
c.add(b1);
c.add(b2);
f.pack();
f.setVisible(true);
