CODEWITHSUNDEEP
javamultithreading
user1050619
user1050619

Reputation: 20896

Anonymous class Threading

I create a anonymous class and pass it to a thread and when I start the thread, it runs its own class..

Can someone explain, what happens to the object-r that is passed to the Thread?

public class Interface1{
    public static void main(String[] args){
        Runnable r = new Runnable(){
            public void run(){
                System.out.println("Cat");
            }
        };

        Thread t = new Thread(r){
            public void run(){
                System.out.println("Dog");
            }
        };

        t.start();


    }
}

Upvotes: 0

Views: 150

Answers (4)

Ashley
Ashley

Reputation: 659

Whenever you start a thread, java.lang.Thread's run() function is called. If you look at the source code of Thread.java, it first checks for the target, which is the Runnable passed in the constructor of the Thread class. This runnable is nothing but your class that has implemented the Runnable interface and thus overridden its run() function.

Since its the run function of the runnable now that is used, you should implement the logic inside your runnable. Keep in mind, that a new OS thread will be only launched by Thread class if target/runnable is not null, otherwise Thread.run() will execute in the same thread as the caller.

Upvotes: 0

ajb
ajb

Reputation: 31699

The javadoc for Thread's run method says:

If this thread was constructed using a separate Runnable run object, then that Runnable object's run method is called; otherwise, this method does nothing and returns.

The javadoc for start says it just calls run. I don't see anything else that runs the Runnable object. So I think we can assume that the only way to run your r object is through the run method of the Thread class. However, you've overridden it.

If you want your overriding run method to also run the r object, consider adding this somewhere in your run:

super.run();

Upvotes: 0

Sotirios Delimanolis
Sotirios Delimanolis

Reputation: 280132

When you pass a Runnable as a constructor argument to Thread, it sets an instance field called target, which it usually uses when it start()s.

But you've overriden Thread#run() which is normally

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

with 

public void run(){
    System.out.println("Dog");
}

In the anonymous class you've created.

So your code runs instead instead of executing target.run() where target is your Runnable instance.

Upvotes: 6

Subhrajyoti Majumder
Subhrajyoti Majumder

Reputation: 41220

If you see the code in Thread.java -

634     public void  [More ...] run() {
635         if (target != null) {
   // target is runnable instance which initialized in constructor
636             target.run();
637         }
638     }

If you pass runnable object through constructor then it executes But here you override the run method of Thread class itself in your Anonymous inner class so it executed overrided method.

Upvotes: 0

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