Thread Ques

[Swati Gupta]

From JQplus
Assume that the class compiles fine.
What will happen if a Worker object is created and it's start method is called?

 public class Worker implements Runnable 
{
   Thread w;
   public void start() 
   {
      w = new Thread(this);
   }
   public void run() 
   {
       System.out.println(" Working..."); 
   }
   /* lot of code */
} 
 

The answer is "nothing will be printed."
But I think we are creating here a new worker object and will be calling its start() method that will call the
run() method and it will print Working .. once?
I don't understand that here we are creating here another thread inside the start method?

[ June 11, 2002: Message edited by: swati gupta ]

[Dave Vick]

swati
The start method in the Thread class does all of the behind scenes work to create a new thread and then calls its run method to get it started. When you oeverride the start method you lose all of that functionality and it will execute as a normal method and do nothing except what you tell it to do. In his case it just creates a new Thread and then returns. the run method is never called.
If you did call the run method in your overloaded start metod it would just execute inline (ie. not as a separate thread).
Hope that helps

[Swati Gupta]

Thanks Dave. This is the first example I came across where we are overriding the start method.

[Gautam Sewani]

Hi Dave,
I dont think the above code overrides the start method.The worker class implements the Runnable interface and the runnable interface doesn't even have a start method.So I dont think it is the case of overriding.
The problem coz of which the thread does not start is because the start method on the Thread is not called.For eg,a one line addition would make the worker class execute the run method.

  
class Worker implements Runnable {
Thread t;
public void start()
{
  t=new Thread(this);
  t.start();
}
public void run()
{
System.out.println("run executed");
}
}

When the start method of this worker class is called,the run method will definitely be executed.
Please correct me if I am wrong

[Swati Gupta]

Thanks Gautam. Here Worker is implementing Runnable so if I create a new Thread and pass a object of Worker class as argument and call a start method on this Thread then it works as shown below

 class Worker implements Runnable{
Thread t;
 public void start(){
   t=new Thread(this);
   //t.start();
  }
  public void run(){
   System.out.println("run executed");
  }
public static void main(String args[]){
new Thread(new Worker()).start();
}
}
 

[ June 12, 2002: Message edited by: swati gupta ]