Confused for threading ?

[chetan deol]

public class ThreadBob extends Thread{

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		Thread a = new ThreadBob();
		Thread b = new ThreadBob();
		Thread c = new ThreadBob();
		a.setName("aa");
		b.setName("bb");
		c.setName("cc");
		
		a.setPriority(Thread.MAX_PRIORITY);
		b.setPriority(Thread.MAX_PRIORITY);
		c.setPriority(Thread.MAX_PRIORITY);
		
		a.start();
		b.start();
		c.start();
	}	
	@Override
	public synchronized void run() {
		// TODO Auto-generated method stub
		StringBuffer a = new StringBuffer("a");
        
		for(int i = 0;i<10;i++)
		{
			System.out.println(Thread.currentThread().getName()+ ": " +i);
		}	
	}
}

Even if i synchronized the method outputn is different

aa: 0
bb: 0
aa: 1
bb: 1
aa: 2
bb: 2
cc: 0
cc: 1
cc: 2
cc: 3
cc: 4
cc: 5
cc: 6
cc: 7
cc: 8
cc: 9
aa: 3
bb: 3
bb: 4
bb: 5
aa: 4
bb: 6
aa: 5
bb: 7
aa: 6
bb: 8
aa: 7
bb: 9
aa: 8
aa: 9

[Vijitha Kumara]

These (Thread a,b & c) are three different threads. When you start them they will run in any order (which JVM will decide). Making run method synchronize won't help. When you start those threads they will run their own run methods (which are from three different ThreadBob objects) , each of those have no relation with other's.

[Parashuram Hallur]

Chetan,

If you are expecting each of the threads to be run sequentially, then the code should be modified as below. Lines 9 - 11.

ThreadBoc tBob = new ThreadBob();

Thread a = new Thread(tBob);
Thread b = new Thread(tBob);
Thread c = new Thread(tBob);    

Since you have created three instances of ThreadBob, they wont interfere each other.

HTH

[chetan deol]

Thanks
Then how that synch block will help me.

[Parashuram Hallur]

chetan dhumane wrote:Thanks
Then how that synch block will help me.

Modifying the code as I suggested will make use of the synchronized and will run sequentially. Otherwise it is not guaranteed to run in a sequence. Please note that if you are synchronizing, in other words acquiring lock, make sure it is on the single object. Otherwise it really does not make sense.

[chetan deol]

Thanks

[Jain Jose]

Chetan

You may be looking for an answer on how synchronized work in run() method. the following discussion will be useful

Thread with synchronized run() method