about thread synchronization

[sharma sachin]

hello friends

class MyThread extends Thread
{
    public  synchronized void fname()
        {
                 for(int i=0;i<5;i++)
                     {
                              System.out.println("started........"+i);
                                      try
                                        {
                                                Thread.sleep(200);
                                        }
                                      catch(Exception e)
                                         {
                                                 System.out.println("exception..."+e);
                                         }
                     }
        }

   

   public void run()
       {
              fname();
          
       }

    public static void main(String[] ar)
       {
                 MyThread m1=new MyThread();
                 MyThread m2=new MyThread();

                 m1.start();
                 m2.start();
       }
}
   

i am not understanding the output of the above program
as i have declared fname() method as synchronized so accrding to me output will be
0,1,2,3,4 for thread1
and 0,1,2,3,4 for thread2
or else i am doing mistake in my code can you explain that how we can achieve the desired output for different threads with the help of suitable example

[Seetharaman Venkatasamy]

If I understood your question, you need to create one object and start two threads *on that one object* .
so, change

MyThread m1=new MyThread();  
MyThread m2=new MyThread();     
m1.start();  
m2.start(); 

to

MyThread m1=new MyThread(); //Create Thread/Runnable Object 
Thread threadOne = new Thread(m1);
Thread threadTwo = new Thread(m1);
threadOne.start();  
threadTwo .start(); 

and observe the output!

[Jesper de Jong]

Yes, you have declared the method to be synchronized, but you have two threads that are using two different MyThread objects.

The first one will synchronize on the first MyThread object, and the second one on the second MyThread object. Since these are separate objects, the two threads will not wait for each other. Synchronizing will make threads wait only if you let both threads synchronize on a shared object. Like this:

public class MyThread implements Runnable {

    public synchronized void fname() {
        for (int i = 0; i < 5; ++i) {
            System.out.println("Thread " + Thread.currentThread().getName() + ": " + i);

            try {
                Thread.sleep(200L);
            } catch (InterruptedException e) {
                System.out.println("Thread " + Thread.currentThread().getName() + ": InterruptedException");
            }
        }
    }

    @Override
    public void run() {
        fname();
    }

    public static void main(String[] args) {
        // Create only one MyThread object
        MyThread obj = new MyThread();

        // Create two threads that share the same object
        new Thread(obj).start();
        new Thread(obj).start();
    }
}

[sharma sachin]

thanks a lot jesper
can you also please tell me that how can we print first name and last name using two different threads on shared object

[Sandeep Kumar B]

Sachin
This should help
Feel free to ask any other question you have

class MyThread implements Runnable  
{  
    public  synchronized void fname()  
        {  
                 for(int i=0;i<5;i++)  
                     {  
                              System.out.println("started........"+i);  
                                      try  
                                        {  
                                                Thread.sleep(200);  
                                        }  
                                      catch(Exception e)  
                                         {  
                                                 System.out.println("exception..."+e);  
                                         }  
                     }  
        }  
  
     
  
   public void run()  
       {  
              fname();  
            
       }  
  
    public static void main(String[] ar)  
       {  
    	/*Un comment this code and it will run two different threads on different object
    	Thread m1 = new Thread(new MyThread(), "thread1");
    	Thread m2 = new Thread(new MyThread(), "thread2");
		*/
    	//Create an object first
    	MyThread objMyThread = new MyThread();
    	Thread m1 = new Thread(objMyThread, "thread1");
    	Thread m2 = new Thread(objMyThread, "thread1");
    	m1.start();
    	m2.start();
    	
       }  
}