Thread FAQ:

Question

Why shold we call wait() from syncronized blocks or methods

Answer 1

If your wait or notify call is the only thing in the synchronized block you aren't using it correctly.
A wait should always be associated with a condition. You wait for some condition to be satisfied and the test of that condition must be in the synchronized block with the wait.
Likewise the changing of the condition governing a wait need to be in the same synchronized block as the notify.
Like this:
// wait
synchronized(monitor) {
    while(!canProceed)
       monitor.wait();
// notify
  synchronized(monitor) {
     canProceed = true;
      monitor.notifyAll();
     }Of course it's not necessarily a boolean field, it could be the empty state of a queue or many other things.
If either the test or the setting of the flag were not synchronized with the wait or notify there would be a possibility of the flag state changing between the test and the wait, leading to an indefinite wait.
Edited by: malcolmmc on Mar 20, 2009 8:59 AM