【JAVA】简单动态交互程序——弹球

import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.JApplet;
import javax.swing.JPanel;
import java.awt.Color;
import java.util.ArrayList;
import java.util.List;
import java.awt.event.*;

public class BounceBall extends Frame {
    
    public static final int BOARD_WIDTH = 540;
    public static final int BOARD_HEIGHT = 570;
    List <Ball> balls = new ArrayList<Ball>(); 
    Image offScreenImage = null;      //双缓冲用的
    
    class Ball {
        int direction = 0;
        int x = 0;
        int y = 0;
        Color color;
        public static final int BALLSIZE = 20;
        public  final  Color[] colors={Color.black,Color.blue,Color.cyan,Color.green,Color.orange,Color.pink,Color.red};
        public void drawBall(Graphics g) {
            if(direction == 1) g.clearRect(x, y-5, 20, 20);
            else g.clearRect(x,y+5,20,20);
            g.setColor(color);
            g.fillOval(x,y,20,20);
        }
        public Ball(int x, int y, int ballcount) {
            this.x = x;
            this.y = y;
            this.direction = 1 ;
            this.color = colors[ballcount%7];
        }
    }
    public void paint(Graphics g) {
        for(int i=0;i<balls.size();i++){
            Ball b = null;
            b=balls.get(i);        
            b.drawBall(g);
        }
    }
    
    //    双缓冲用的
    @Override
    public void update(Graphics g)  {
        if(offScreenImage == null){
            offScreenImage = this.createImage(BOARD_WIDTH, BOARD_HEIGHT);
        }
        Graphics gOffScreen = offScreenImage.getGraphics();
        Color c  = gOffScreen.getColor();
        gOffScreen.setColor(Color.LIGHT_GRAY);
        gOffScreen.fillRect(0, 0, BOARD_WIDTH, BOARD_HEIGHT);
        gOffScreen.setColor(c);
        paint(gOffScreen);
        g.drawImage(offScreenImage, 0, 0, null);
        for(int i=0;i<balls.size();i++){
            if(balls.get(i).y> BOARD_HEIGHT-Ball.BALLSIZE) balls.get(i).direction=0;
            if(balls.get(i).y< Ball.BALLSIZE)  balls.get(i).direction=1;
            if(balls.get(i).direction==1) balls.get(i).y+=5;
            if(balls.get(i).direction==0) balls.get(i).y-=5;
        }
    }
    //    重画
    private class PaintThread implements Runnable {
        
        public void run() {
            try {
            while(true){
                repaint();
                Thread.sleep(50);
                } 
            }catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }    
    }
    
    private class MouseMonitor extends MouseAdapter{
        public void mouseClicked(MouseEvent e) {
            int x = e.getX();
            int y = e.getY();
            Ball b = new Ball(x,y,balls.size());
            balls.add(b);
        }
    }
    
    public void launchFrame() throws Exception{
        
        //界面初始化
        this.setLocation(100, 50);
        this.setSize(BOARD_WIDTH, BOARD_HEIGHT);
        this.setResizable(false);
        this.setBackground(Color.LIGHT_GRAY);
        setVisible(true);
    
        //重画
        new Thread(new PaintThread()).start();

        this.addMouseListener(new MouseMonitor());
        
        this.addWindowListener(new WindowAdapter(){
            public void windowClosing (WindowEvent e){
                System.exit(0);
            }
        });
        
    }
    public static void main(String[] args)throws Exception {
         new BounceBall().launchFrame();
    }
}