小球撞墙

import java.awt.*;

public class MyBall{

public static void main(String[] args){

Frame w = new Frame();

w.setSize(300, 400);

MyPanel mp = new MyPanel();

w.add(mp);

Thread t = new Thread(mp);

t.start();

w.show();

}

}

class MyPanel extends Panel implements Runnable{

int x = 30;

int y = 30;

int att = 0;

public void paint(Graphics g){

g.fillOval(x, y, 20, 20);

}

public void run(){

while(true){

//定义飞行姿态

if(att == 0){

x++;

y++;

}

if(att == 1){

x--;

y++;

}

if(att == 2){

x--;

y--;

}

if(att == 3){

x++;

y--;

}

//改变飞行姿态

if(x > 263){

if(att == 0){

att = 1;

}else{

att = 2;

}

}

if(y > 341){

if(att == 1){

att = 2;

}else{

att =3;

}

}

if(x < 0){

if(att == 2){

att = 3;

}else{

att = 0;

}

}

if(y < 0){

if(att == 3){

att = 0;

}else{

att = 1;

}

}

try{

Thread.sleep(30);

}catch(Exception e){

}

repaint();

}

}

}