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pauleen pauleen

Joined: Aug 31, 2004
Posts: 3
This question was taken from
Whats the correct answer for this and why.
Can anyone explain to me.

Which of the following keywords indicates a thread is releasing its Object lock?

1) release
2) wait
3) continue
4) notifyAll
Julian Kennedy
Ranch Hand

Joined: Aug 02, 2004
Posts: 823
Hmmm, well out of those four only "continue" is a keyword in the sense of being a reserved word in Java, but that's not the answer.

The correct answers are wait and notifyAll, which are methods on java.lang.Object. Check out the relevant sections of the Javadoc for Object. You may also find this page from the Threads section of Sun's Java Tutorial useful.

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Joyce Lee
Ranch Hand

Joined: Jul 11, 2003
Posts: 1392
The answer is wait.

* release is not a Thread method.
* continue is a Java keyword. But it has nothing to deal with Thread.
* By calling notify(), it doesn't mean that the thread has given up its lock at the moment. The lock is only released when the thread has moved out of the synchronized code.
* By calling wait(), the thread gives up its lock on the object immediately.

This is a SCJP question. If you're now preparing for SCJP, I highly recommend the book Sun Certified Programmer & Developer for Java 2 Study Guide (Exam 310-035 & 310-027) by Kathy Sierra and Bert Bates.

[ September 05, 2004: Message edited by: Joyce Lee ]
Julian Kennedy
Ranch Hand

Joined: Aug 02, 2004
Posts: 823
Hmmm, Joyce is right. Subtle point about notifyAll(); it's typically the last thing you do in a synchronized block. Probably why I only scored 80% on my SCJP!
Ernest Friedman-Hill
author and iconoclast

Joined: Jul 08, 2003
Posts: 24199

Moving to Threads and Synchronization forum for any further discussion.

[Jess in Action][AskingGoodQuestions]
I agree. Here's the link:
subject: Threads
It's not a secret anymore!