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What is the advantage of using Condition interface/implementations over the conventional wait notify mechanism? Here I quote the comments written by Doug Lea:
Condition factors out the Object monitor methods (wait, notify and notifyAll) into distinct objects to give the effect of having multiple wait-sets per object, by combining them with the use of arbitrary Lock implementations. Where a Lock replaces the use of synchronized methods and statements, a Condition replaces the use of the Object monitor methods.
I see this is a more Object Oriented way of implementing wait/notify mechanism. But is there a sound advantage over the former?
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The wait() method causes the current thread to wait until another thread invokes the notify() or notifyAll() methods for that object. The notify() method wakes up a single thread that is waiting on that object's monitor. The notifyAll() method wakes up all threads that are waiting on that object's monitor.
Calling notify() or notifyAll() methods issues a notification to a single or multiple threads that a condition has changed and once the notification thread leaves the synchronized block, all the threads which are waiting for fight for object lock on which they are waiting and lucky thread returns from wait() method ...
In case of multiThreading notify() method sends the notification to only one thread among the multiple waiting threads which are waiting for lock. While notifyAll() methods in the same context sends the notification to all waiting threads instead of single one thread.
If you need to call wait(), notify(), or notifyAll() from within a non-synchronized method, then you must first obtain a lock on the object's monitor. If you don't, an exception will be generated when an attempt is made to call the method in question.
The biggest problem is that wait/notify is error prone for new developers. The main problem is not knowing how to handle them correctly can result is obscure bug.
Condition wraps up this functionality into a dedicated component, however it behaves much the same.
There is a question regarding wait/nofity posted minutes before this one and many, many more Search [java]+wait+notify
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