CODEWITHSUNDEEP
javamultithreading
anubhav deshwal
anubhav deshwal

Reputation: 136

confusion while creating a thread by extending thread class

we knew that we can create a new thread by creating a new class thats extends thread and then to create an instance of that thread..while going through this topic i saw an example in my book which is as follows.

 class NewThread extends Thread{
    NewThread(){
        super("demo thread");
        System.out.println("child thread:"+this);
        start();
    }
    public void run(){
        try{
            for(int i=5;i>0;i--){
                System.out.println("child thread"+i);
                Thread.sleep(500);
            }
         } catch(InterruptedException e){
             System.out.println("child interrupted");
         }
         System.out.println("exiting child thread");
      }
  }

in this example i am able to understand all those things except the constructor part in which we are not using any instance(thread) to call start().so my question is how the start() method is called without any thread.

Upvotes: 1

Views: 96

Answers (4)

Ravindra babu
Ravindra babu

Reputation: 38910

Below code is responsible for calling start() method on your NewThread instance in NewThread constructor, which calls start() method in Thread class, which calls run() method. 

 NewThread(){
    super("demo thread");
    System.out.println("child thread:"+this);
    start();
}

Flow:

NewThread() -> start() -> Thread start() -> native start0() ->  run()

Refer to this SE question for internals of Thread class start() method :

What's the difference between Thread start() and Runnable run()

Upvotes: 0

Dimitris P.
Dimitris P.

Reputation: 383

You are inheriting the start() method from the class Thread that your NewThread class extends. So you can call it like any other method.

Same goes for the run() method which could use the @Override annotation in order to make the concept of inheritance clearer.

@Override
public void run() {
        try{
            for(int i = 5; i > 0; i--) {
                System.out.println("child thread" + i);
                Thread.sleep(500);
            }
        } catch(InterruptedException e) {
           System.out.println("child interrupted");
        }
        System.out.println("exiting child thread");
    }

Upvotes: 1

Artem Larin
Artem Larin

Reputation: 162

This start() method is called on the thread instance, which has just been created in this constructor.

Upvotes: 0

redMist
redMist

Reputation: 229

It is valid because method start() is inherited from Thread class, so you can call it like any other class method.

Upvotes: 0

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