I've had a test, and there was a question I lost some points on, because I wasn't able to answer it :

Which of the following is NOT a condition which can cause a thread to block :

• Calling an objects's wait() method
• Waiting for an I/O operation
• Calling sleep()
• Calling yield()
• Calling join()

As far as I know, all of these are blocking calls :

• wait() returns when an something calls notify(), blocks until then
• If the thread is WAITING for an I/O operation then it's obviously blocked
• sleep(), obviously, blocks until the time runs out, or something wakes up the thread
• yield() "cancels the rest of the thread's timeslice" (lacking a better term), and returns only when the thread is active again
• join() blocks until the thread it's waiting for terminates.

Am I missing something here?