Query on threads ?

[gurpeet singh]

if i have something like this

Thread t = new MyThread(Runnable);
public void run(){}
t.start();

here "Runnable" is target runnable object and MyThread class extends from Thread. when t.start() is called whether it will invoke run method of Thread class or the runnable passed in the constructor of MyThread and why ?

[Helen Ma]

Thread t = new MyThread(Runnable) won't compile.
Maybe , you can define a class that implements Runnable interface and provid a run method for this class.
For example,

public class Work implements Runnable {

   public void run(){ ....}
}

When t.start() is invoked, the thread will execute the run method defined in Work class.

Thread class itself implements Runnable interface. You can define a run method for your MyThread class.
You can do this :

  Thread t = new MyThread();
            t.start() ; //will invoke the run method of the MyThread class.

[ujjawal rohra]

Hi Gurpreet

In your case Literally writing Runnable in the statement
Thread t = new MyThread(Runnable) will give compiler error as Helen suggested as Runnable is an interface in java.lang package.
You need to change the name of the object passed in the constructor of MyThread and then calling start() will invoke the run method defined in the class of that object and remember that the class should be implementing Runnable interface..


Hope that helps!!!

[Md. Minhajur Rahman]

gurpeet singh wrote:if i have something like this

Thread t = new MyThread(Runnable);
public void run(){}
t.start();

here "Runnable" is target runnable object and MyThread class extends from Thread. when t.start() is called whether it will invoke run method of Thread class or the runnable passed in the constructor of MyThread and why ?

Hi gurpeet, Do you mean this kind of scenery accordingly following program?

class MyRunnable implements Runnable {
	   public void run(){
		   System.out.println("Runnable Run method  is called.......");
	   }
	}
class MyThread extends Thread
{
	Thread t;
	public MyThread(Runnable r) {
		t=new Thread(r);
	}
	public void run()
	{
		System.out.println("MyThread Run method is called......");
		//t.start();
	}
}

public class ThreadTest
{
	public static void main(String[] args)
	{
		Thread t=new MyThread(new MyRunnable());
		t.start();
	}
}

If you wonna mean this, then when t.start() is called at line 24, then it will invoke run method of MyThread class. If you want to this start method will call MyRunnable's Run method, Then you have to call it yourself in run method of MyThread class according line 15. Only Then MyRunnable's Run will be called. If you pass a runnable instance to a Thread class accordingly line 10, when you call t.start() which in turns calls Runnable's Run Method, not Thread's Run method.

[Seetharaman Venkatasamy]

gurpeet singh wrote:

Thread t = new MyThread(Runnable);
public void run(){}
t.start();

here "Runnable" is target runnable object and MyThread class extends from Thread. when t.start() is called whether it will invoke run method of Thread class or the runnable passed in the constructor of MyThread and why ?

well, here you are passing the Runnable object to Thread class and when you say t.start this calls the Thread's run method and it execute the run method of Runnable.
from Thread class

public void run() {
if (target != null) {
target.run();
}
}

target is nothing but Runnable you are delegating to Thread.