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posted 1/19/2011 8:38:51 AM

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Author notifyAll() example

Swerrgy SmithRanch Hand

Joined: Mar 26,2010Posts: 52

Dear all,

In the book of K&B, there is an example about how to use notifyAll() for thread

communication. However, in the class Calculator below, if I remove the

notifyAll(), the program stills works well. Can anybody tell me why?

view pla in c opy to clipboard print ?

Note: T ext content in the code block s is automatically word-wrapped

01. publicclass Reader extends Thread {

02. Calculator c;

03.

04. public Reader(Calculator calc) {

05. c = calc;

06. }

07.

08. publicvoid run() {

09. synchronized(c) {

10. try {

11. System.out.println("Waiting for calculation

...");

12. c.wait();
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posted 1/20/2011 8:37:34 AM

Joined: Dec 27,2010Posts: 35

and notifyAll()? I understood serialization was not longer on the exam and I am

familiar with the updated objectives. Is there anything new on the exam that is

not covered in K&B SCJP 6? Sorry if this is out of scope of the topic. I have been

studying threads a lot for the exam...regardless I know it will be helpful in the

real world but my focus is to pass the exam.

OCPJP for Java 6 on 01/2011

Sunny JainRanch Hand

Joined: Jul 23,2007Posts: 433

I like...

This is actually a very simple example.

3 threads are running all on same instance, which means - synchronized(this)

means same for all threads. Lets say we have T-1, T-2,T-3 as threads and C-1 is

calculator instance. Let assume that -

> T-2 got the lock over C-1, this leads to T-1 and T-3 both on waiting stage.

> T-2 finishes the calculation and released the lock over C-1. Now you can do

either of two things-1) Notify all the other threads waiting for C-1, by calling C-1.notifyAll( ) or

this.notifyAll( ). order of T-1 and T-3 will be random. could be either T-1 then T-3

or vice versa.

2) Leave it as it is, in this case JVM will schedule the running of threads by its

own. order of T-1 and T-3 will be random. could be either T-1 then T-3 or vice

versa.

Thanks,

Thanks and Regards,SCJP 1.5 (90%), SCWCD 1.5 (85%), The Jovial Java,java.util.concurrent tutorial

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Code using notifyAll() runs indefinitely

notify() vs notifyAll() in this code

Doubt w ith notify/ notifyAll method

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