Question

Let’s look at the following code, it’s working exactly.

final class DemoThread
{
    public void temp()
    {
        new Thread(new Runnable()
        {
            public void run()
            {
                System.out.println( "Isn't it great ?" ) ;
            }
        } ) .start() ;
    }
}

final public class Main
{
    public static void main(String[] args)
    { 
        new DemoThread().temp();
    }
}

It works fine and displays the message Isn’t it great ? on the console. The only question here is that why the Runnable interface need not be implemented by the class DemoThread?

Answer 1

Runnable is being implemented by the anonymous inner class within the temp method:

new Thread(new Runnable()
{
    public void run()
    {
        System.out.println( "Isn't it great ?" ) ;
    }
} ) .start() ;

Given that an instance of DemoThread isn’t being passed into the Thread constructor, whether or not it implements Runnable is completely orthogonal to how the thread runs.

Your code is a similar to this:

final class DemoThread
{
    public void temp()
    {
        new Thread(new Anonymous()).start();
    }

    private class Anonymous implements Runnable
    {
        public void run()
        {
            System.out.println( "Isn't it great ?" ) ;
        }
    }
}

Does that make it clearer for you?