Possible Duplicate:
Why wait should always be in synchronized block
I noticed, the Thread wait() method needs to be called inside either in a synchronized code block or in the synchronized method. Without that, it is throwing
java.lang.IllegalMonitorStateException
. Why?
Please refer to the javadoc for Object.wait.
http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/Object.html#wait()
"The current thread must own this object's monitor. The thread releases ownership of this monitor and waits until another thread notifies threads waiting on this object's monitor to wake up either through a call to the notify method or the notifyAll method. The thread then waits until it can re-obtain ownership of the monitor and resumes execution."
From The Java Tutorials
public synchronized guardedJoy() {
// This guard only loops once for each special event, which may not
// be the event we're waiting for.
while(!joy) {
try {
wait();
} catch (InterruptedException e) {}
}
System.out.println("Joy and efficiency have been achieved!");
}
Why is this version of guardedJoy synchronized? Suppose d is the object we're using to invoke wait. When a thread invokes d.wait, it must own the intrinsic lock for d — otherwise an error is thrown. Invoking wait inside a synchronized method is a simple way to acquire the intrinsic lock.
The error you have is the error they are referring to in the example.
@synchronized(Obj) {...} is like:
SynchronizedObject.lock() ... SynchronizedObject.Unlock()
wait is basically short for:
SynchronizedObject.Unlock() & SynchronizedObject.Lock()
that makes it clearer IMO .... you need to have the lock to be able to release it
