Question

I am trying to understand below program. If I call new ReaderThread().start() it is working fine, but if I call new ReaderThread().run(), the application goes into an infinite loop. What is the difference?

public class Contention {

    private static boolean ready;
    private static int number;

    private static class ReaderThread extends Thread {
        public void run() {
                 while (!ready){
                System.out.println("ready ..."+ready);
                Thread.yield();}
            System.out.println(number);
           // }
        }
    }


    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        new ReaderThread().run();
        number = 42;
        ready = true;

    }

}

Answer 1

If you use new ReaderThread().start();,you are creating actually a new thread instance which will run in the background and main() resumes with its further execution.

But new ReaderThread().run(); creates an instance of this class and makes a normal method call to the run() method, so the main() has to wait till the run() has finished executing and returned the control back to main(), which in your case is an infinite loop.

If you want to start a new thread then start by using ReaderThread().start(); this is the correct way to start a thread, there are no alternatives for this.