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