Extending Thread Chaos

[Sahil Kapoor]

Consider the following code

  class TestThreads {

  public static void main(String... args) {
    
    Runnable r = new Runnable() {
      
      public void run() {
        System.out.println("I got Threads");
      }
    };
    
    new MyThread(r).start();  // I am not clear about threads yet    .......1
   
    
    ((Thread) new MyThread(r) ).start(); //I am not clear about threads yet............2
  }
}

class MyThread extends Thread {
  
  MyThread(Runnable r) {
    super(r);
  }
  
 
  public void run() {
    System.out.println("I am not clear about threads yet");
  }
}  

1 : In the above code i am making the Thread class Object with the Runnable instance but still getting unexpected output.
2: I upcasted it, still getting the same output.

My expected Output is : "I got Threads " but it is not

Thanks !!!

[Ankit Garg]

Look at this discussion (there were many other discussions like that too in the past)...

[Sahil Kapoor]

It is not clear from the linked discussion.....That why it is all happening.....

Moreover i upcasted it.....even then it is not working.....

[Sahil Kapoor]

      public class Thread implements Runnable{  
        Runnable runnable;  
        public Thread(Runnable other) {  
            runnable = other;  
        }  
        //some more code  
       public void run() {  
         if(runnable != null) {   \\\  Line no 1
               runnable.run();  
           }  
       }  
   }    

This is how Thread class is implemented , then if i passing "runnable" to Thread class.....Its run method should be called as Line 1 in the above code says.....

[Henry Wong]

Sahil Kapoor wrote:
This is how Thread class is implemented , then if i passing "runnable" to Thread class.....Its run method should be called as Line 1 in the above code says.....

Hint: When you override a method, which version of the method will get called?

Henry

[Sahil Kapoor]

You are right Henry , But i am making Thread object by passing Runnable object, and according to book, if we pass runnable, runnable's run method would be invoked.

[Sahil Kapoor]

Ooooppppssss Got it ..........FInally !!!
Thanks Henry !!!
Cheers!!!

[Sahil Kapoor]

@ For others.... who got confused.....IMO implementation (partial) is as follows

   public class Thread implements Runnable{
   
  Runnable r;
  
  Thread(Runnable target){ r = target;}
   
  public void run() { 
    
    if( r !=null)
      r.run();
  }

  
  public void start() {
  
    // Some native work

    this.run();
  }

}


 

[Suresh Babu Venkat]

Sahil Kapoor wrote:

  Runnable r = new Runnable()    

That line of the program should have given a compile time error as we cannot instantiate an interface.

[Sahil Kapoor]

Suresh Babu Venkat wrote:

Sahil Kapoor wrote:

  Runnable r = new Runnable()    

That line of the program should have given a compile time error as we cannot instantiate an interface.

If you have covered Anonymous classes then i am using that.

If you have not done then, i am not creating an instance of runnable , in fact i am creating an instance of class that implements runnable and the implementig class body is defined after new Runnable {//here}.

Thanks!!!

[Henry Wong]

Sahil Kapoor wrote:

 
  public void start() {
  
    // Some native work

    this.run();
  }
}
 

I know that this is only supposed to be "explanation" code, but I have to point out that this part is not true.

The start() method, or the thread that called the start() method, does not call the run() method. The start() method creates a new thread, and part of the process, after start up, of the newly created thread, is to call the run() method.

Henry

[Suresh Babu Venkat]

Sahil Kapoor wrote:If you have covered Anonymous classes then i am using that.

If you have not done then, i am not creating an instance of runnable , in fact i am creating an instance of class that implements runnable and the implementig class body is defined after new Runnable {//here}.

ooopssss... I overlooked it.... thanks for the explanation.

[Sahil Kapoor]

@ Henry , yess your right , IS the following pseudocode fine now :-

  public void start() {  
     
     // Some native work to JVM to create new thread of execution 
   
   
     // Pass this to JVM too, so that it could call run method of this .
  }  
 }