Question

I have 2 classes. One method of the class calls the other class’ method, but it has to wait until the method finishes to proceed to the execution of the rest of the code.

This is a rough code of what I’m trying to make. And I know this doesn’t work.

public class Example 
{
    Thread thread;

    public Example(Thread thread)
    {
        this.thread = thread;
    }

    public void doSomethingElse()
    {
        System.out.println("Do something else");
        thread.notify();
    }
}

public class Example2 
{
    Thread thread;
    Example example;

    public Example2()
    {
        example = new Example(thread);
        thread = new Thread()
        {
            public void run()
            {
                example.doSomethingElse();
                try {
                    this.wait();
                } catch (InterruptedException ex) {                    
                }
                System.out.println("Do something");
            }
        };
    }

    public void doSomething()
    {
        thread.run();
    }
}

Now do you know how to make this right?

Answer 1

Not sure if your constrained to using this particular approach (wait/notify) however a better approach is taking advantage of the Java Concurrency API

public class ExampleCountDownLatch
{
    public void doSomething () throws InterruptedException
    {
        final CountDownLatch latch = new CountDownLatch(1);

        Thread thread = new Thread()
        {
            public void run ()
            {
                System.out.println("do something");
                latch.countDown();
            }
        };

        System.out.println("waiting for execution of method in your example class");
        thread.start();
        // wait for reasonable time otherwise kill off the process cause it took
        // too long.
        latch.await(3000, TimeUnit.MILLISECONDS);

        // now I can do something from your example 2
        System.out.println("now i can execute from example 2 do something else");
    }
}

Anyway just another approach if you had an option.

UPDATE:

Here is a blog about this very topic.