Java | PTA练习：弹球

题目要求

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

 参考代码

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Rectangle2D;
import java.util.ArrayList;
import javax.swing.*;

public class Main
{
    public static void main(String[] args){
        EventQueue.invokeLater(new Runnable()
        {
            public void run(){
                JFrame frame = new BounceFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setVisible(true);
            }
        });
    }
}
//小球弹跳
class BallRunable implements Runnable
{
    private Ball ball;
    private Component component;
    public static final int STEPTS = 1000;
    public static final int DELAY = 5;
    public BallRunable(Ball aBall,Component aComponent){
        ball = aBall;
        component = aComponent;
    }
    public void run(){
    try{
        for(int i=1;i<=STEPTS;i++)
        {
            ball.move(component.getBounds());
            component.repaint();
            Thread.sleep(DELAY);
        }
    }
    catch(InterruptedException e){
        }
    }
}
//定义窗体
class BounceFrame extends JFrame{
    private BallComponent comp;
    public static final int DEFAULT_WIDTH = 450;
    public static final int DEFAULT_HEIGHT = 350;
    public static final int STEPS = 1000;
    public static final int DELAY = 3;
    public BounceFrame(){
        setSize(DEFAULT_WIDTH,DEFAULT_HEIGHT);
        setTitle("弹球");

        comp = new BallComponent();
        add(comp,BorderLayout.CENTER);

        JPanel buttonPanel = new JPanel();
        addButton(buttonPanel,"开始",new ActionListener()
        {
            public void actionPerformed(ActionEvent event)
            {
                addBall();
            }
        });
        addButton(buttonPanel,"结束",new ActionListener()
        {
            public void actionPerformed(ActionEvent event)
            {
                System.exit(0);
            }
        });
        add(buttonPanel,BorderLayout.SOUTH);    
    }
    public void addButton(Container c,String title,ActionListener listener)
    {
        JButton button = new JButton(title);
        c.add(button);
        button.addActionListener(listener);
    }
    public void addBall(){
        Ball b = new Ball();
        comp.add(b);
        Runnable r = new BallRunable(b,comp);
        Thread t = new Thread(r);
        t.start();
    }
}
//定义小球
class Ball
{
    private static final int XSIZE = 15;
    private static final int YSIZE = 15;
    private double x = 0;
    private double y = 0;
    private double dx =1;
    private double dy = 1;
    public void move(Rectangle2D bounds){
        x += dx;
        y += dy;
        if(x < bounds.getMinX()){
            x = bounds.getMinX();
            dx = -dx;
        }
        if(x + XSIZE >= bounds.getMaxX())
        {
            x = bounds.getMaxX() - XSIZE;
            dx = - dx;
        }
        if(y < bounds.getMinY())
        {
            y = bounds.getMinY();
            dy = - dy;
        }
        if(y + YSIZE >= bounds.getMaxY())
        {
            y = bounds.getMaxY() - YSIZE;
            dy = -dy;
        }
    }

    public Ellipse2D getShape()
    {
        return new Ellipse2D.Double(x,y,XSIZE,YSIZE);
    }
}
//定义小球显示窗体
class BallComponent extends JPanel{
    private ArrayList<Ball> balls = new ArrayList<Ball>();
    public void add(Ball b)
    {
        balls.add(b);
    }
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        for(Ball b : balls)
        {
            g2.fill(b.getShape());
        }
    }
}