关于notifyAll()问题

Question

不是说notifyAll()是让所有挂起线程恢复的吗？下面代码怎么只恢复了其中t51的线程。。。

class A5 implements Runnable
{ int i=0;
String name;
public void run()
{ while(true)
{ i++;
System.out.println(name+"Z="+i);
if(i==5){
try{ 挂起线程A5();}
catch(Exception e){}

}
try{ Thread.sleep(1000);}
catch(Exception e){}
}
}
public synchronized void 挂起线程A5() throws InterruptedException
{ wait();

}
public synchronized void 恢复线程A5()
{ notifyAll();

}
}

public class Example15
{ public static void main(String args[])
{ int m=0;
A5 t51=new A5(); //线程A5的目标对象
t51.name="张一";

Thread thread=new Thread(t51);
thread.setName(t51.name);

     A5 t52=new A5();    //线程A5的目标对象 
     t52.name="张二";     
     Thread thre=new Thread(t52);
     thre.setName(t52.name);


     thre.start();
     thread.start();

     while(true) 
     { m++;
       System.out.println("我是主线程m="+m);
       if(m==10)
        { System.out.println("让全部线程继续工作");
          try {  
              t51.恢复线程A5(); }                     
          catch(Exception e){} 
          break; 
        }
        try{ Thread.sleep(1000);  } 
        catch(Exception e){}
     }
  }

}

Answer 1

[code="java"]public class Example15 {
public static void main(String args[]) {
int m=0;
Object oo = new Object();
A5 t51=new A5(); //线程A5的目标对象
t51.name="张一";

t51.synchronizedObject = oo;
Thread thread=new Thread(t51);
// thread.setName(t51.name);

    A5 t52=new A5();    //线程A5的目标对象 
    t52.name="张二";     
    t52.synchronizedObject = oo;
    Thread thre=new Thread(t52); 

// thre.setName(t52.name);

    thre.start();
    thread.start(); 

    while(true) {
        m++;
        System.out.println("我是主线程m="+m); 
        if(m==10) {
            System.out.println("让全部线程继续工作"); 
            try {t51.恢复线程A5();} catch(Exception e){} 
            break;
        }
        try {Thread.sleep(1000);} catch(Exception e){} 
    }
} 

}

class A5 implements Runnable {
Object synchronizedObject;
int i=0;
String name;
public void run() {
while(true) {
i++;
if(i==5) {
System.out.println(name+" 挂起.");
try{挂起线程A5();} catch(Exception e){}

} else {
System.out.println(name+"Z="+i);
}
try{Thread.sleep(1000);} catch(Exception e){}

        if(i==15) {
            System.out.println(name+" 完成."); 
            break;
        }
    }
}
public void 挂起线程A5() throws InterruptedException { 
    synchronizedObject.wait();
}

public void  恢复线程A5() {
    synchronizedObject.notifyAll();  
}

}
[/code]

1，多线程中常见的问题：wait、notify、notifyAll必须针对同一个同步对象，不显式指定同步对象，同步对象为This，t51的this和t52的this当然不同。

2，我直接传入的一个相同的同步对象给两个线程，就好了。