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

{

E．xample3_4 example;

boolean isHold;

C．ounter (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＞

＜BO