Thread: Not calling run method

Question

I am new in java. Can someone help me why it is not calling Run method. Thanks in advance.

package com.blt;

public class ThreadExample implements Runnable {
    public static void main(String args[])
    {       

        System.out.println("A");
        Thread T=new Thread();
        System.out.println("B");
        T.setName("Hello");
        System.out.println("C");
        T.start();
        System.out.println("D");
    }

public void run()
{
    System.out.println("Inside run");

}
}

score 6 · Accepted Answer · answered Feb 11 '13 at 09:09

6

You need to pass an instance of ThreadExample to the Thread constructor, to tell the new thread what to run:

Thread t = new Thread(new ThreadExample());
t.start();

(It's unfortunate that the Thread class has been poorly designed in various ways. It would be more helpful if it didn't have a run() method itself, but did force you to pass a Runnable into the constructor. Then you'd have found the problem at compile-time.)

answered Feb 11 '13 at 09:09

Jon Skeet

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I think in the very early days of Java there was a tendency to supply the run method by extending Thread, rather than passing a Runnable. That depended on Thread implementing Runnable, and therefore having a run method. – Patricia Shanahan Feb 11 '13 at 09:14
@PatriciaShanahan: Absolutely - it was a bad idea then, too :) It's nice that best practice has moved on... it's a shame that we're stuck with badly-designed libraries forever... – Jon Skeet Feb 11 '13 at 09:15

score 2 · Answer 2 · answered Feb 11 '13 at 09:09

The run method is called by the JVM for you when a Thread is started. The default implementation simply does nothing. Your variable T is a normal Thread, without a Runnable 'target', so its run method is never called. You could either provide an instance of ThreadExample to the constructor of Thread or have ThreadExample extend Thread:

new ThreadExample().start();
// or
new Thread(new ThreadExample()).start();

score 0 · Answer 3 · answered Feb 11 '13 at 09:56

You can also do it this way.Do not implement Runnable in your main class, but create an inner class within your main class to do so:

class TestRunnable implements Runnable{
    public void run(){
        System.out.println("Thread started");
   }
}

Instantiate it from your Main class inside the main method:

TestRunnable test = new TestRunnable(); 
Thread thread = new Thread(test);
thread.start();

Thread: Not calling run method

3 Answers3

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