问答题
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＞
【参考答案】
①stop.addActionListener(new ActionListener(){②class Counter ......
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