Synchronizing on main method arguments

[ujjawal rohra]

In the code below, in the main method I am synchronizing on the String array parameter of the main method. The code gives an IllegalMonitorStateException when trying to call wait on commented line.

class Test extends Thread{
public void run(){
		synchronized (this) {
			System.out.println("thread run");
			notify();
		}
}
public static synchronized void main(String[] args) {
		Test e=new Test();
		synchronized (args) {
			try {
				e.wait(); //exception
			} catch (InterruptedException e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			}
		}
		e.start();
		System.out.println("In main");
	}

}

I know that a thread has to be owner of the object on which it is synchronizing but in this case I am unable to figure out the reason of this exception as to how main thread is not the owner of the array.
Probably I could not understand the conditions as to when a thread owns an object's lock. Please clarify.

[Matthew Brown]

"Being the owner" means "owning the synchronization lock" in this case. So you can only call wait() on an object inside a block synchronized on that object.

Here you synchronize on args, but you call wait() on e. The thread doesn't have a lock on e.

[ujjawal rohra]

Ohh yes I missed that the object on which wait is called should be the same on which the block is synchronized.

Thanks Matthew .