用Java实现写字板功能！

import java.awt.Color;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionAdapter;

import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JRadioButton;

public class TestEventMouse extends JFrame{
Container contentPanel; //内容格引用
JButton a1,a2,a3,a4,a5;//按钮
JRadioButton backGroundRadio,foreGroundRadio; //定义两个单选框
ButtonGroup radioGroup; //单选按钮组
int xValue,yValue; //保留鼠标位置（x,y）
JFrame jf=this;
public TestEventMouse(){ //构造函数
super("写字板");
a1=new JButton("Black");//实现五个按钮
a2=new JButton("Blue");
a3=new JButton("Red");
a4=new JButton("White");
a5=new JButton("Yellow");
contentPanel=this.getContentPane();//获取内容格
contentPanel.setLayout(new FlowLayout());//设置内容格的布局管理器
backGroundRadio=new JRadioButton("backGround"); //实例化复选框
foreGroundRadio=new JRadioButton("foreGround");
contentPanel.add(backGroundRadio);//添加到内容格里面去
contentPanel.add(foreGroundRadio);
contentPanel.add(a1);//添加按钮
contentPanel.add(a2);
contentPanel.add(a3);
contentPanel.add(a4);
contentPanel.add(a5);
MouseListenerHandler mou=new MouseListenerHandler(); //实现一个事件监听类
a1.addMouseListener(mou); //注册为五个按钮的监听者
a2.addMouseListener(mou);
a3.addMouseListener(mou);
a4.addMouseListener(mou);
a5.addMouseListener(mou);
radioGroup=new ButtonGroup(); //实例单选按钮组
radioGroup.add(backGroundRadio);//将两个radio按钮构成一个组
radioGroup.add(foreGroundRadio);

addMouseMotionListener( //匿名类
new MouseMotionAdapter(){ //因为是当前一个对象调用，所以搞了个适配器玩玩
public void mouseDragged(MouseEvent e){
xValue=e.getX();
yValue=e.getY();
repaint(); //调用paint()方法
}
}
);
setSize(500,500);
setVisible(true); //设置可见
}
public class MouseListenerHandler implements MouseListener{ //鼠标事件监听类
public void mousePressed(MouseEvent e){
if(e.getSource()==a1){ //用getSouce()获取对象
if(backGroundRadio.isSelected())
contentPanel.setBackground(Color.BLACK);//用内容格来设置背景色
else
jf.setForeground(Color.BLACK); //用Frame框架来设置前景色
}
if(e.getSource()==a2){
if(backGroundRadio.isSelected())
contentPanel.setBackground(Color.BLUE);
else
jf.setForeground(Color.BLUE);
}
if(e.getSource()==a3){
if(backGroundRadio.isSelected())
contentPanel.setBackground(Color.RED);
else
jf.setForeground(Color.RED);
}
if(e.getSource()==a4){
if(backGroundRadio.isSelected())
contentPanel.setBackground(Color.WHITE);
else
jf.setForeground(Color.WHITE);
}
if(e.getSource()==a5){
if(backGroundRadio.isSelected())
contentPanel.setBackground(Color.YELLOW);
else
jf.setForeground(Color.YELLOW);
}
}
public void mouseClicked(MouseEvent e) {
}
public void mouseEntered(MouseEvent e) {
}
public void mouseExited(MouseEvent e) {
}
public void mouseReleased(MouseEvent e) {
}
}

public void paint(Graphics g){
g.fillOval(xValue, yValue, 4, 4);
}
public static void main(String args[]){
new TestEventMouse();
}
}