Java课程设计，多色弹弹球

package cn.hncu.MyThread2;

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSpinner;
import javax.swing.Timer;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class BallsJFrame2 extends JFrame implements ChangeListener,ActionListener{
	
	//这些变量需要做事件监听，因此不能放在构造方法里面
	private JSpinner spinner;
	private RollBalls ball;
	private JButton btn1,btn2;
	
	public BallsJFrame2(){
		super("Rolling balls");
		this.setBounds(400, 200, 700, 600);
		this.setDefaultCloseOperation(EXIT_ON_CLOSE);//设置关闭窗口的功能
		this.setResizable(false);//设置窗口不能拉大拉小，true为能够拉伸
		Color colors[]={Color.black,Color.blue,Color.cyan,Color.DARK_GRAY,Color.green,
				Color.red,Color.magenta,Color.orange,Color.pink,Color.yellow};//为每一个球设置颜色
		
		//建立球的对象，同时会将整个画布添加进去
		ball=new RollBalls(100, colors);
		this.getContentPane().add(ball);
		
		JPanel panel=new JPanel();
		this.getContentPane().add(panel,"South");
		panel.add(new JLabel("delay"));
		spinner=new JSpinner();
		spinner.setValue(100);
		panel.add(spinner);
		spinner.addChangeListener(this);
		
		btn1=new JButton("start");
		btn1.setEnabled(false);
		btn1.addActionListener(this);
		panel.add(btn1);
		
		btn2=new JButton("stop");
		btn2.addActionListener(this);
		panel.add(btn2);
		
		this.setVisible(true);
	}
	
	public static void main(String[] args) {
		new BallsJFrame2();
	}

	@Override
	public void stateChanged(ChangeEvent e) {
		int value=Integer.parseInt(""+spinner.getValue());
		ball.setDelay(value);
	}

	@Override
	public void actionPerformed(ActionEvent e) {
		if (e.getSource()==btn1) {
			btn1.setEnabled(false);
			btn2.setEnabled(true);
			ball.setStart();
		}
		if (e.getSource()==btn2) {
			btn1.setEnabled(true);
			btn2.setEnabled(false);
			ball.setStop();
		}
	}
}

class RollBalls extends Canvas implements ActionListener{
	private Balls balls[];
	private int delay;
	private Timer timer;
	public RollBalls(int delay,Color colors[]){
		this.delay=delay;
		balls=new Balls[colors.length];
		
		//将每一个球对象的位置和大小确定
		for (int i = 0,x=40; i < balls.length; i++,x+=20) {
			balls[i]=new Balls(x, x, colors[i]);
		}
		timer=new Timer(delay, this);
		timer.start();//启动线程
	}
	
	public void setDelay(int delay){
		timer.setDelay(delay);
	}
	
	public void setStop(){
		timer.stop();
	}
	
	public void setStart(){
		timer.restart();
	}
	
	@Override
	public void paint(Graphics g) {
		for (int i = 0; i < balls.length; i++) {
			g.setColor(balls[i].color);
			
			balls[i].x=balls[i].left? balls[i].x-10:balls[i].x+10;
			if (balls[i].x<=0||balls[i].x>=this.getWidth()-20) {
				balls[i].left=!balls[i].left;
			}
			
			balls[i].y=balls[i].up? balls[i].y-10:balls[i].y+10;
			if (balls[i].y<=0||balls[i].y>=this.getHeight()-20) {
				balls[i].up=!balls[i].up;
			}
			
			g.fillOval(balls[i].x, balls[i].y, 20, 20);
		}
	}
	
	class Balls{
		private int x,y;
		private Color color;
		private boolean left,up;
		
		public Balls(int x,int y,Color color){
			this.x=x;
			this.y=y;
			this.color=color;
			left=up=false;
		}
	}


	@Override
	public void actionPerformed(ActionEvent e) {
		repaint();
	}
}