小球滚动

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Arc2D;
import java.util.Random;

import javax.swing.*;

class jj extends JFrame {
}

public class jumpball extends JFrame {

 protected long sleepAmount = 10;

 public jumpball() {

  setBackground(Color.CYAN);
  Toolkit kit = Toolkit.getDefaultToolkit(); // 定义工具包
  Dimension screenSize = kit.getScreenSize(); // 获取屏幕的尺寸
  int screenWidth = screenSize.width; // 获取屏幕的宽
  int screenHeight = screenSize.height; // 获取屏幕的高
  setLocation(new Point(screenWidth / 2 - getWidth() / 2, screenHeight / 2 - getHeight() / 2));
  setDefaultCloseOperation(EXIT_ON_CLOSE);
  JButton mb = new JButton();
  mb.setText("click");
  JPanel pan = new JPanel();
  pan.setBackground(Color.CYAN);
  pan.setLayout(new FlowLayout());
  pan.add(mb);
  setSize(500, 500);
  final Mypaint mp = new Mypaint();
  // mp.setBackground(Color.BLACK);
  add(mp);

  getContentPane().add(pan, BorderLayout.NORTH);
  mb.addActionListener(new ActionListener() {

   @Override
   public void actionPerformed(ActionEvent e) {
    Thread tt = new Thread(new Runnable() {

     @Override
     public void run() {
      // TODO Auto-generated method stub

      try {
       while (true) {
        mp.repaint();
        Thread.sleep(sleepAmount);
       }
      } catch (InterruptedException e) {
       // TODO Auto-generated catch block
       e.printStackTrace();
      }
     }
    });
    tt.start();
   }
  });

 }

 public static void main(String[] args) {
  jumpball my = new jumpball();
  my.setVisible(true);
 }
}

class Mypaint extends JPanel {
 int x = 15, y = (int) (Math.random() * 1000 % getHeight());
 double radius = 15;
 int step = 5;
 double k = Math.random() * Math.PI * 2;

 public Mypaint() {
  setDoubleBuffered(true);
 }

 @Override
 public void paint(Graphics g) {
  // TODO Auto-generated method stub
  super.paint(g);
  
  if (x < 0 || x > getWidth() - radius * 2) {
//   if (k <= Math.PI)
    k = -k + Math.PI * 2;
   // if (k < 0)
   // k = 2 * Math.PI + k;
  } else if (y < 0 || y > getHeight() - radius * 2) {
   k = Math.PI - k;
   
  }

  x += Math.sin(k) * step;
  y += Math.cos(k) * step;
  Arc2D arc = new Arc2D.Float(1);
  arc.setFrame(x, y, radius * 2, radius * 2);
  arc.setAngleExtent(360);
  Graphics2D g2 = (Graphics2D) g;
  g2.setColor(Color.BLUE);
  g2.fill(arc);

 }

}