Java Multithreading Class Methods?

Question

I am relativity new to multithreading in Java, and I would like to know if it is possible to execute a method within a class in parallel. So instead of this:

public void main() {
  this.myMethod();
  this.myMethod();
}

... where each method within the class is fired after the previous call has finished, that they would be done in parallel. I know the following example can be done, but that involves creating new classes, which I would like to avoid:

public class HelloRunnable implements Runnable {
  public void run() {
    System.out.println("Hello from a thread!");
  }

  public static void main(String args[]) {
    (new Thread(new HelloRunnable())).start();
  }
}

Just to be clear, I have seen this example, but it was of no help me to me.

Is the key to cracking this issue involve using public static methods? Either way, could someone please provide an example how to do this with their solution?

Thank you for your time!

Ernest Friedman-Hill · Accepted Answer · 2011-12-10 01:14:30Z

4

Sorry, can't be done according to your restrictions. You can't run anything in a Java thread without creating a Thread object, and something to contain the run() method: either a separate class that implements Runnable, or a class that extends Thread. The question you pointed to shows exactly what to do; there's no "better" answer, nor indeed any other answer.

answered Dec 10, 2011 at 1:14

Ernest Friedman-Hill

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1 Comment

Oliver Spryn Over a year ago

Ah... alright. Guess I'll just end up using a bit more code. :) Thanks, Ernest!

Julius Musseau · Accepted Answer · 2011-12-10 01:34:22Z

I'd probably do it like this. The CountDownLatch and Executors classes are handy utilities from Java 5 to make this kind of stuff easier. In this particular example the CountDownLatch will block main() until both parallel executions have completed.

(So to answer your question: it's even worse than you thought! You have to write even MORE code!)

ExecutorService EXECUTOR_SERVICE = Executors.newCachedThreadPool();

public void main() {
  final CountDownLatch cdl = new CountDownLatch(2); // 2 countdowns!
  Runnable r = new Runnable() { public void run() {
    myMethod();
    cdl.countDown();
  } };

  EXECUTOR_SERVICE.execute(r);
  EXECUTOR_SERVICE.execute(r);

  try {
    cdl.await();
  } catch (InterruptedException ie) {
    Thread.currentThread().interrupt();
  }
}

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