Thread execution

[joshua antony]

public class Whiz extends Thread{
private int value=9;
public static void main(String[] args)
{
Whiz whiz = new Whiz();
whiz.run();
 
System.out.println("before the thread is started:   "+whiz.value);
whiz.start();
System.out.println("The value of the integer variable is:   "+whiz.value);
}
public void run()
{
value++;
}
}

The output is:

before the thread is started: 10
The value of the integer variable is: 10

Why value is not increemented second time?

[Kalpesh Jain]

Probably, you were not very lucky....
As soon as you call whiz.start(); a new thread comes to life (other one is your main thread). Now, in your case, before the new thread could reach value++; thread scheduler gave chance to the main thread to run, and the main thread completed the stmt ' System.out.println("The value of the integer variable is: "+Temp.value);' before value is actually incremented.
Again, this may not be the case always.
Just try and put Thread.sleep(100); after whiz.start() and you'll see the difference. Hope that clears.

[Prabhu Venkatachalam]

Because, Before Second Thread( whiz.start(); ) starts and runs, Main method ends.

Try this, this works,

    
 
public class Whiz extends Thread{
private int value=9;
public static void main(String[] args)
{
Whiz whiz = new Whiz ();
whiz.run();
whiz.start();
}
public void run()
{
value++;
System.out.println("The value of the integer variable is:   "+value);
}
}
 

[Sanjeev Singh]

Being specific to the problem,

public class Whiz extends Thread{
 private int value=9;
 public static void main(String[] args)
 {
  Whiz whiz = new Whiz();
  whiz.run();
  System.out.println("before the thread is started:   "+whiz.value);
  whiz.start();
  System.out.println("The value of the integer variable is:   "+whiz.value);
 }
 public void run()
 {
  value++;
 }
}  

whiz.run() will not create a new execution thread.Calling the run method will simply execute the target(in the run() mehod of the Thread class),which in this case is null.So calling of this method will have no effect.
whiz.start() will create a new execution thread.But it is upto the scheduler who is going to decide the time to execute the new target... the value of the value may or may not increment after this method call.

[Rohit Dhodapkar]

Hi Prabu,

Can you please explain what to do to make sure that the main thread finshes its execution only after the thread in the code???

[Barry Gaunt]

Sanjeev Kumar Singh: "Calling the run method will simply execute the target(in the run() mehod of the Thread class),which in this case is null.So calling of this method will have no effect."

The above is wrong. Calling whiz.run() will execute the run method of the Whiz instance referenced by whiz. So the instance variable value is incremented and printed. The thing is, it is done in the context of the main thread not the newly created thread.