Doubt in Threads Synchronization

[Balaji Bang]

public class MyThread1  extends Thread{


	public static void main(String[] args) {
		MyThread1 s=new MyThread1();
		s.start();
		
		MyThread1 s1=new MyThread1();
		s1.start();
	}
	public void run() {
               getTotal();
	
}
public synchronized void getTotal(){
	for(int i=0;i<10;i++){
		System.out.println(Thread.currentThread().getName()+" "+i);
	}
}
}

For this I got the output as :
Thread-0 0
Thread-1 0
Thread-0 1
Thread-1 1
Thread-0 2
Thread-1 2
Thread-0 3
Thread-1 3
Thread-0 4
Thread-1 4
Thread-0 5
Thread-1 5
Thread-0 6
Thread-1 6
Thread-0 7
Thread-1 7
Thread-0 8
Thread-1 8
Thread-0 9
Thread-1 9

My Doubt is : when the first Thread 's' has been started in gets the lock on the getTotal synchronized method. Then no other Thread can enter that method. but why the output is showing a mix of both Threads??
But if I run the same codeby implementing Runnable then Then Thread 1 is running after the Thread 0 has been completed.

What is the difference ???

[ramesh maredu]

Output is mixed because you are executing two threads which are created from two different objects so synchronization can not be achieved.

Post your code with Runnable interface, if code is same like above (creating two objects) it also should not give expected output.

[Ganeshkumar cheekati]

hi banu
please use code tags

[Balaji Bang]

Yes you are right. I made a mistake by passing same runnable target to both threads.

public class MyThread1  implements Runnable{


	public static void main(String[] args) {
		MyThread1 s=new MyThread1();
		Thread t=new Thread(s);
		t.start();
		
		MyThread1 s1=new MyThread1();
		Thread t1=new Thread(s);    //[b] I passed the first instance only[/b]
		t1.start();
	}
	public   void run() {
               getTotal();
	
}
public synchronized void getTotal(){
	for(int i=0;i<10;i++){
		System.out.println(Thread.currentThread().getName()+" "+i);
	}
}
}

Here t and t1 are having same Runnable target. If so then we will get Thread1 runs after Thread0 has completed? If we have two threads running on different objects we will get a mix.
Synchronization means only one thread( on single object) can access the method at a time.
how can we create two threads on same object when we are extending a Thread class.