Slightly confused about notify method

Question

Hi,
I'm currently studying for the SCJP exam and have 2 questions about the thread notify call.
(1) Is it possible when a thread owns an object lock, i.e. say in synchronized code, that it can call the notify method on a particular thread. For example, say there are 2 threads, names thread1 and thread2, and thead1 obtains object lock, can it call Thread2.notify()? The reason I'm read conflicting web-pages, saying it isn't possible for 1 thread to notify another thread and it is up to Object to decide which thread to invoke, say must use notifyAll() or notify() call. Is this true?
(2) Which thread in following code is Thread.sleep() referring to? Is it the main thread that created 2 threads?
class running extends Thread
     public void run(){
public class fredFlintStone{     
     public static void main(String[] args) {
          running  thread1 = new running();
          running thread2 = new running();
          thread1.start();
          thread2.start();
          try
          //confused here     
        Thread.sleep(12L);
          catch(InterruptedException e)
}Cheers!

Answer 1

its best not to confuse terminology here.
marktheman wrote:
I ... have 2 questions about the thread notify call.Thread is an object which has a notify() method. However you should never use it. You should only use notify() on regular objects.
(1) Is it possible when a thread owns an object lock, A Thread holds a lock, see [http://java.sun.com/javase/6/docs/api/java/lang/Thread.html#holdsLock(java.lang.Object)]
i.e. say in synchronized code, that it can call the notify method on a particular thread. A thread calls notify() on an object not a given thread. (Unless that object is a thread, but don't do that!)
For example, say there are 2 threads, names thread1 and thread2, and thead1 obtains object lock, can it call Thread2.notify()?It can, but it would fail as you can only call notify() on an object you hold the lock to.
The reason I'm read conflicting web-pages, saying it isn't possible for 1 thread to notify another thread It is possible but not in any useful way.
and it is up to Object to decide which thread to invoke,The Object has no say in the matter, its up to the scheduler in the OS.
say must use notifyAll() or notify() call. Is this true?no.
(2) Which thread in following code is Thread.sleep() referring to? The javadoc says "Causes the currently executing thread to sleep". You should always check the documentation for asking that sort of question.