A doubt on Multiple Threads and the "join()" method !!

[radhakrishnan jankiraman]

Hi !!
I understand muli-threading as "parallel instances of execution" and i have a query in this regard. The following is a code and its output. I would like to how will you describe "what exactly is the join() method doing here?".

<font size=2.5>
class NewThread implements Runnable{
 String name;
 Thread t;
 NewThread(String threadname){
  name = threadname;
  t = new Thread(this,name);
  System.out.println("New thread: "+t);
  t.start();
  }
  public void run(){
   try{
    for(int i=5;i>0;i--){
     System.out.println(name + ":" + i);
     Thread.sleep(1000);
     }
    }
   catch(InterruptedException e){
    System.out.println(name + "Interrupted.");
    }
   }
 }
class DemoJoin{
 public static void main(String args[]){
  NewThread ob1 = new NewThread("One");
  NewThread ob2 = new NewThread("Two");
  NewThread ob3 = new NewThread("Three");
  System.out.println("Thread One is Alive:"+ ob1.t.isAlive());
  System.out.println("Thread Two is Alive:"+ ob2.t.isAlive());
  System.out.println("Thread Three is Alive:"+ ob3.t.isAlive());
  try{
   System.out.println("Waiting for threads to finish.");
    ob1.t.join();
    ob2.t.join();
    ob3.t.join();
    }
  catch(InterruptedException e){
   System.out.println("Main thread Interrupted");
   }
  System.out.println("Finished all the threads!!");
  }
}

And the output is:
New thread: Thread[One,5,main]
New thread: Thread[Two,5,main]
New thread: Thread[Three,5,main]
Thread One is Alive:true
Thread Two is Alive:true
Thread Three is Alive:true
Waiting for threads to finish.
One:5
Two:5
Three:5
One:4
Two:4
Three:4
One:3
Two:3
Three:3
One:2
Two:2
Three:2
One:1
Two:1
Three:1
Finished all the threads!!

Now is'n't it misleading to say that " join() waits until the thread on which it is called terminates. " ?
What it actually does is that it does not let the thread "from which it is being called" terminate,
till the thread "on which it is being called" terminates
The important thing to note is that after a call to join() in main, the control passes to the next join() and so on.
But it does not come out of the try{}catch{} block , as is evident from the last print statement. Thats seems like "magic".
Please enlighten me on this.
Thanx and Regards !!
radhakrishnan. j
(edited by Cindy to format code)
[This message has been edited by Cindy Glass (edited November 28, 2001).]

[Peter den Haan]

Originally posted by radhakrishnan jankiraman:
Now is'n't it misleading to say that " join() waits until the thread on which it is called terminates. " ? What it actually does is that it does not let the thread "from which it is being called" terminate, till the thread "on which it is being called" terminates

The second description would certainly be more misleading than the first. The join() call doesn't merely prevent the calling thread from terminating - it simply blocks until the Thread it is called on terminates. This is also why your "Finished all the threads" message displays only when all three threads have terminated. The join() calls don't complete until their respective threads are dead.
- Peter