用线程控制图片的交替显示

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class game5 extends JFrame {
static JLabel label;
String path = "E:/pic/";
static Icon p1, p2, p3;
static Boolean start;
public game5() {
  this.setTitle("石头剪子布");
  this.setSize(600, 300);
  this.setVisible(true);
  Container c = this.getContentPane();
  c.setLayout(new GridLayout(1, 3));
  JButton b1 = new JButton("start");
  JButton b2 = new JButton("over");
  label = new JLabel();
  c.add(b1);
  c.add(b2);
  c.add(label);
  p1 = new ImageIcon(path + "g.gif");
  p2 = new ImageIcon(path + "o.gif");
  p3 = new ImageIcon(path + "p.gif");
  b1.addActionListener(new start(""));
  b2.addActionListener(new over());
  this.addWindowListener(new WindowAdapter() {
   public void windowClosing(WindowEvent e) {
    System.exit(0);
   }
  });
}
class start extends Thread implements ActionListener {
// 添加构造函数
  public start(String name) {
   super(name);
  }
  public void actionPerformed(ActionEvent e) {
   game5.start = true;
// 问题中这里创建的三个线程是Thread空对象
   Thread t1 = new start("t1");
   Thread t2 = new start("t2");
   Thread t3 = new start("t3");
   t1.start();
   t2.start();
   t3.start();
  }
  synchronized void set() {
   while (start) {
// 使用equals比较对象
    if (this.getName().equals("t1")) {
     game5.label.setIcon(p1);
    }
    if (this.getName().equals("t2")) {
     game5.label.setIcon(p2);
    }
    if (this.getName().equals("t3")) {
     game5.label.setIcon(p3);
    }
   }
  }
  public void run() {
   set();
  }
}
class over implements ActionListener {
  public void actionPerformed(ActionEvent e) {
   game5.start = false;
  }
}
public static void main(String args[]) {
  new game5();
}
}
为什么在程序运行后，图片交替显示的速度越来越慢，最后好长时间才更换一张，甚至不动了，窗口也关闭不了了线程 swing

补充：Java ,  Java SE