编写一个窗体的类BallFrameDemo:

package com.lzy.ball;

import javax.swing.JFrame;

public class BallFrameDemo extends JFrame {

JFrame

frame; public

BallFrameDemo(){ frame=new

JFrame(); } public void

showSony(){ frame.setSize(800, 600);

frame.setTitle("多个小球的碰壁反弹");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setResizable(false); //禁止最大化

frame.setLocationRelativeTo(null); //居中显示

BallPanelDemoA panel=new

BallPanelDemoA();

Thread td=new

Thread(panel);

td.start();

frame.add(panel);

frame.setVisible(true);

}

public static void main(String[] args)

{ new

BallFrameDemo().showSony();

}

}

编写一个面板类BallPanelDemoA：

package com.lzy.ball;

import java.awt.Color;

import java.awt.Graphics;

import java.util.Random;

import javax.swing.JPanel;

public class BallPanelDemoA extends JPanel implements Runnable

{

Random random;

BallDemo[] balls;

int

size=6; //设置小球的个数

public BallPanelDemoA(){

random=new Random();

balls=new BallDemo[size];

for(int

i=0;i

balls[i]=new

BallDemo(random.nextInt(700),random.nextInt(500),20+i*2,new

Color(random.nextInt(255),random.nextInt(255),random.nextInt(255)));

}

}

@Override

public void paint(Graphics g) {

super.paint(g);

this.setBackground(Color.BLUE);

for(int

i=0;i

balls[i].draw(g);

}

}

@Override

public void run() {

while(true){

for(int i=1;i

for(int j=0;j

balls[i].setPanel(this);

balls[i].move();

balls[j].setPanel(this);

balls[j].move();

if(balls[i].twoBallisHit(balls[j])){ //当两球相撞时，把一个球的半径设为0，相当于消失了，看不见了;

balls[i].setR(30);

balls[j].setR(0);

}

}

}

try {

Thread.sleep(50);

} catch

(InterruptedException e) {

//

TODO Auto-generated catch block

e.printStackTrace();

}

repaint();

}

}

}

把小球封装在BallDemo中：

package com.lzy.ball;

import java.awt.Color;

import java.awt.Graphics;

import javax.swing.JPanel;

public class BallDemo {

private int x;

private int y;

private int r;

private Color color;

private JPanel panel;

private int flag=0;

public static final int

LEFT_DOWN=0; //小球的运行轨迹为左下：x++;y++

public static final int

LEFT_UP=1; //小球的运行轨迹为左上：x++;y--

public static final int

RIGHT_DOWN=2; //小球的运行轨迹为右下：x--;y++

public static final int

RIGHT_UP=3; //小球的运行轨迹为右上：x--;y--

public BallDemo(){}

public BallDemo(int x, int y, int r, Color color)

{ //通过写一个带参数的构造方法，方便BallDemo的对象把值传进来;

this.setX(x);

this.setY(y);

this.setR(r);

this.setColor(color);

}

public int getX() {

return x;

}

public void setX(int x) {

this.x = x;

}

public int getY() {

return y;

}

public void setY(int y) {

this.y = y;

}

public int getR() {

return r;

}

public void setR(int r) {

this.r = r;

}

public Color getColor() {

return color;

}

public void setColor(Color color) {

this.color = color;

}

public JPanel getPanel() {

return panel;

}

public void setPanel(JPanel panel) {

this.panel = panel;

}

public int getFlag() {

return flag;

}

public void setFlag(int flag) {

this.flag = flag;

}

public void draw(Graphics

g){ //在小球的自己类里面画小球，方便在外面调用数组获取多个小球;

g.setColor(color);

g.fillOval(x, y, 2*r,

2*r);

} public void

move(){ //每个小球都有自己的move()方法，用来判断自己的位置;

switch (this.flag) {

case LEFT_DOWN:

x++;

y++;

if(x>panel.getWidth()-2*r){

this.flag=RIGHT_DOWN;

}

if(y>panel.getHeight()-2*r){

this.flag=LEFT_UP;

}

break;

case LEFT_UP:

x++;

y--;

if(x>panel.getWidth()-2*r){

this.flag=RIGHT_UP;

}

if(y<0){

this.flag=LEFT_DOWN;

}

break;

case RIGHT_DOWN:

x--;

y++;

if(y>panel.getHeight()-2*r){

this.flag=RIGHT_UP;

}

if(x<0){

this.flag=LEFT_DOWN;

}

break;

case RIGHT_UP: