下面程序是一个计时器，从1000秒开始倒计时，直到为0结束。在界面上有两个按钮，一个可以暂停计时，另一个可以继续已经暂停的计时。请更正题中带下划线的部分。
注意：不改动程序的结构，不得增行或删行
import java.awt.*;
import java.awt.event.*;
import java.applet.Applet;
public class Example3_4 extends Applet
public Color color = Color.red;
private int num= 1000;
public Counter theCounter;
private Button stop;
private Button start;
public void init()
stop = new Button("暂停");
start = new Button ("继续");
theCounter = new Counter(this);
stop.addActionListener(new Lst() implements ActionListener
public void actionPerformed(ActionEvent e)
theCounter.sus();
);
start.addActionListener(new SuspenListener());
add(start);
add(stop);
theCounter.start();
public void paint(Graphics g)
g.setCotor(color);
g.drawString(String.valueOf(num),50,50);
public void setInt(int i)
num=i;
class SuspenListener implements ActionListener
public void actionPerformed(ActionEvent e)
theCounter.conti ();
public class Counter extends Thread
Example3_4 example;
boolean isHold;
Counter (Example3_4 ex)
this.example = ex;
isHold = false;
public void sus()
isHold = true;
public synchronized void conti()
isHold = false;
notify();
public void run()
for (int i = 1000; i＞0; i--)
if (i%2 == 1)
example.color = Color.red;
else
example.color = Color.blue;
example.setInt(i);
example.repaint();
try
sleep(1000);
synchronized
while(isHold)
wait ( );
catch (InterruptedException ie)
＜HTML＞
＜HEAD＞
＜TITLE＞Example3_4＜/TITLE＞
＜/HEAD＞
＜BODY＞
＜applet code="Example3_4.class" width=300 height=400＞
＜/applet＞
＜/BODY＞
＜/HTML＞