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synchronization, wait and notify

susana miranda
Greenhorn

Joined: May 21, 2008
Posts: 9
Hello, I have a question. In the following code:

class ThreadC extends Thread{
public static void main(String [] args) {
new ThreadC().metodo1();
}

public synchronized void metodo1()
{
ThreadC b = new ThreadC();
b.start();
// synchronized(b) {
try {
System.out.println("Waiting for b to complete...");
b.wait();
} catch (InterruptedException e) {System.out.println("Error al hacer b.wait()");}
System.out.println("metodo1 terminado");
// }
}

public synchronized void run( ) {
// synchronized(this) {
System.out.println("run into ThreadB");
notify( );
System.out.println("Ya se hizo notify()");
try{
Thread.sleep(2000);
}
catch(InterruptedException e){}
System.out.println("ya se libera el lock de ThreadB");
}
// }
}

At runtime: metodo1 generates IllegalMonitorstateException, as far as I now this is because wait() must be called in a synchronized context.
1. Why isn't enough to make metodo1() synchronized?
2. Why notify() works well in run() method just by making it synchronized?

Ankit Garg
Sheriff

Joined: Aug 03, 2008
Posts: 9321
    
  17

Hi Susana. Welcome to javaranch

1. method1 generated IllegalMonitorStateException because you are calling wait on object b

b.wait();

and method1 is synchronized on this.



2. it works in run method because you are calling notify on this reference. Since the method run is synchronized, and you call notify without using any reference variable, so it will be called on this. So the code will work as



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susana miranda
Greenhorn

Joined: May 21, 2008
Posts: 9
Hi Ankit, I saw my mistake. Thanks!
 
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