Java Applet实现红色反弹球程序

编写图形界面程序，显示一个红色反弹球的程序，当该球撞击Applet边框时，它应从边框弹回并以相反方向45°运动。

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.applet.*;

class MyPanel extends JPanel implements Runnable {
	ThreadDome ud = null;

	public MyPanel() {
		ud = new ThreadDome();
		Thread t = new Thread(ud);
		t.start();
	}

	public void paint(Graphics g) {
		super.paint(g);
		setBackground(Color.white);
		setForeground(Color.white);
		g.fillOval(0, 0, 20, 20);
		this.drawBall(ud.ball.getX(), ud.ball.getY(), ud.ball.getWidth(), ud.ball.getHeight(), g);
	}

	public void drawBall(int x, int y, int width, int height, Graphics g) {
		g.setColor(Color.red);
		g.fillOval(x, y, width, height);
	}

	public void run() {
		while (true) {
			try {
				Thread.sleep(5);
			} catch (Exception e) {
				e.printStackTrace();
			}
			this.repaint();
		}
	}
}

class Ball {
	int x;
	int y;
	int width;
	int height;
	int x_speed = 2;
	int y_speed = 2;

	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 getWidth() {
		return width;
	}

	public void setWidth(int width) {
		this.width = width;
	}

	public int getHeight() {
		return height;
	}

	public void setHeight(int height) {
		this.height = height;
	}

	public Ball(int x, int y, int width, int height) {
		this.x = x;
		this.y = y;
		this.width = width;
		this.height = height;
	}
}

class ThreadDome implements Runnable {
	Ball ball = new Ball(100, 200, 20, 20);

	public void run() {
		while (true) {
			try {
				Thread.sleep(5);
			} catch (Exception e) {
				e.printStackTrace();
			}
			ball.x += ball.x_speed;
			ball.y += ball.y_speed;
			if (ball.getX() > 400 || ball.getX() < 0) {
				ball.x_speed = -ball.x_speed;
			}
			if (ball.getY() > 400 || ball.getY() < 0) {
				ball.y_speed = -ball.y_speed;
			}
		}
	}
}

public class Homework04 extends JFrame {
	MyPanel p = null;

	public static void main(String[] args) {
		Homework04 experiment = new Homework04();
	}

	public Homework04() {
		setTitle("弹弹球窗口");
		p = new MyPanel();
		Thread ud = new Thread(p);
		ud.start();
		this.add(p);
		this.setSize(400, 400);
		this.setVisible(true);
		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	}
}