The methods notify, notifyAll, and wait should only be called by a thread that is the owner of the object's monitor (intrinsic lock). In other words, the methods should only be called from within a synchronized statement or method. Otherwise the method call will throw IllegalMonitorStateException.

Ensure that calls to notify, notifyAll, or wait are called from within a synchronized statement or method.

In the following example, the methods produce and consume use wait and notifyAll to communicate. However, the consume method is not synchronized, so the calls to wait and notifyAll will always throw an exception.

To fix this example, add the synchronized keyword to the declaration of the consume method.

J. Bloch. Effective Java (second edition), p. 276. Addison-Wesley, 2008.

Java API Specification: Object.notify(), Object.notifyAll(), Object.wait(), Object.wait(long).