java 后台线层也叫守护线层

import java.util.concurrent.locks.*;
class Do9
{
public static void main(String[] args)
{
Ds d=new Ds();
Thread t1=new Thread(d);
Thread t2=new Thread(d);
Thread t3=new Thread(d);
t1.start();
t2.start();
t3.setDaemon(true);//变成后台线层，要在start()之前
t3.start();

for (int i=0; i<9999;i++ )
{
if(i==9997)
{
t1.interrupt();
t2.interrupt();
break;
}
System.out.println(i);
}
}
}
class Ds implements     Runnable
{

private boolean flag=true;
public synchronized void run()
{
while(flag)
{
try{wait();}catch(InterruptedException e){System.out.println(Thread.currentThread().getName()+"..."+e);}
System.out.println(Thread.currentThread().getName()+"哈哈");
break;
}

}
public void setFlag()
{
flag=false;
}
}