编写程序，该程序通过一个发射按钮可以发射一个弹球，该球遇到边界时会自动弹回，在移动固定次数后，该球停止运动。要求每次点击发射按钮都会发射一个弹球，如果点击多次，则多个弹球同时运动。该程序通过另一个结束可以结束程序的运行。参考界面如图所示。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.Random;
import java.awt.geom.*;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

//装球的容器
class Box extends JPanel{
   private ArrayList<Ball>all=new ArrayList<>();
   public void add(Ball tp){
      all.add(tp);
   }

   // 绘制all中所有的球
   public void paintComponent(Graphics g){
      super.paintComponent(g);
      Graphics2D x=(Graphics2D)g;
      for(Ball tp:all){
         // x.draw(tp.generateball());
         x.setColor(tp.getc());
         x.fill(tp.generateball());
      }
   }
}

class Ball{
   private int w=20,h=20;   //用于绘制椭圆
   private int x=0,y=0;    //定位球坐标
   private int dx=1,dy=1;  //坐标增量
   private int rx,gx,bx;
   public Ball(){
      Random rd=new Random();
      rx=rd.nextInt(250);gx=rd.nextInt(250);bx=rd.nextInt(250);
      w=(int)(Math.random()*20)+20;
      h=w;
   }
   public Color getc(){
      return new Color(rx,gx,bx);
   }
   public void move(int minx,int maxx,int miny,int maxy){
      x+=dx;
      y+=dy;
      //越界处理
      Random rd=new Random();
      int mdx=rd.nextInt(2)+1;
      int mdy=rd.nextInt(2)+1;
      if(x+w>maxx){
         x=maxx-w;
         dx=-mdx;  //反方向走
      }
      if(x-w<minx){
         x=minx+w;
         dx=mdx;
      }
      if(y+h>maxy){
         y=maxy-h;
         dy=-mdy;  //反方向走
      }
      if(y-h<miny){
         y=miny+h;
         dy=mdy;
      }
   }
   public Ellipse2D generateball(){
      return new Ellipse2D.Double(x,y,w,h);
   }
}

class ballmove implements Runnable{
   private Ball tb;
   private Box tbox;
   private static final int gap=5;
   public ballmove(Ball bx,Box bbx){
      tb=bx;
      tbox=bbx;
   }
   public void run(){
      try{
         while(true){
            tb.move(0, tbox.getWidth(), 0, tbox.getHeight());
            tbox.repaint();
            Thread.sleep(gap);
         }
      }
      catch (Exception e){
         e.printStackTrace();
      }
   }
}

class Mwid extends JFrame{
   private Box box=new Box();
   private static final int width=600;
   private static final int height=500;
   public Mwid(){
      setSize(width, height);
      setTitle("弹球程序");
      // setLayout();
      JPanel btnbox=new JPanel();
      JButton beg=new JButton("开始");
      JButton end=new JButton("结束");
      add(box);
      btnbox.add(beg);
      btnbox.add(end);
      add(btnbox,BorderLayout.SOUTH);
      beg.addActionListener(new handlee(1));
      end.addActionListener(new handlee(2));
      
   }
   public void addBall(){
      Ball nb=new Ball();
      box.add(nb);
      // Runnable t1=new
      Thread t1=new Thread(new ballmove(nb,box));
      t1.start();
   }
   //处理按钮事件
   class handlee implements ActionListener{
      int type;
      handlee(int s){
         type=s;
      }
      public void actionPerformed(ActionEvent e){
         if(type==1) addBall();
         else System.exit(0);
      }
   }
}

public class Main{
   public static void main(String[] args) {
      Mwid mf=new Mwid();
      mf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      mf.setVisible(true);
   }
}