Thread Question---start()

[Huifen Lu]

Hi all,

What will happen when you attempt to compile and run the following code?
class MyThread extends Thread
{
            public void run()
            {
                        System.out.println("MyThread: run()");
            }
            public void start()
            {
                        System.out.println("MyThread: start()");
            }
}
class MyRunnable implements Runnable
{
            public void run()
            {
                        System.out.println("MyRunnable: run()");
            }
           public void start()
            {
                        System.out.println("MyRunnable: start()");
            }
}
public class MyTest 
{
            public static void main(String args[])
            {
                        MyThread myThread  =  new MyThread();
                        MyRunnable myRunnable = new MyRunnable();
                        Thread thread  =  new Thread(myRunnable);
                        myThread.start();
                        thread.start();
            }
}    

A. Prints : MyThread: start() followed by MyRunnable:run()
B. Prints : MyThread: run() followed by MyRunnable:start()
C. Prints : MyThread: start() followed by MyRunnable:start()
D. Prints : MyThread: run() followed by MyRunnable:run()
E. Compile time error
F. None of the above

Can someone please explain in detail why the answer is A instead of D?
Thanks a lot in advance!

Huifen

[Henry Wong]

Basically, the MyThread class overrides the start() method. When you call the start() method, it prints the start message. It doesn't actually start a thread that calls the run() method -- that code has been overridden.

Henry

[Huifen Lu]

Henry, thanks for your reply, I got it.

[cs singh]

Hi Henry, can u please explain it in detail, i did not get the explaination.., i think choice sd be A.

[Henry Wong]

Originally posted by cs singh:
Hi Henry, can u please explain it in detail, i did not get the explaination.., i think choice sd be A.

Not sure what are you asking... You agree with me that it is choice A, but you don't understand why I think it is choice A?

BTW, why do you think it is choice A?

Henry

[Anindya Saha]

The answer should be A
MyThread class overrides the start() method. So when myThread.start() is called it calls the overridden start() method in MyThread class and not the start() method of Thread class beacsue the reference variable type is MyThread. Hence it will print
MyThread: start()
MyRunnable class does not override start() method. Its just any other method. Now Thread thread = new Thread(myRunnable); creates a new thread from myRunnable. Calling thread.start(); will look for Thread class' start method beacsue the reference variable type is Thread which would eventually try to call MyRunnable's run method.Hence it will print
MyRunnable: run()