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While creating threads I see code like:-

Runnable watdaheck = new Runnable()
{
System.out.println("java with time contradicts itself");
}

From what I know an interface cannot be instantiated so I fail to understand how we can write Runnable() for creating anonymous class. An interface can be given a reference but cannot be instantiated is what we are taught in polymorphism.

Prabhat Gaur
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    Note that the thing that's like an interface but that you can instantiate is a _class_, not an object. I think you meant to ask if Runnable is an interface or a class. See [this question](https://stackoverflow.com/questions/9224517/what-are-classes-references-and-objects/9224971) for more. – yshavit May 31 '19 at 02:21

3 Answers3

6

Runnable is interface, you are creating an anonymous class which implements the Runnable interface.

Basil Bourque
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xingbin
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2

I just modify a bit your code.

 Runnable watdaheck = new Runnable()
    {    
         public void run(){
             System.out.println("java with time contradicts itself");
         }
    }

The right part 

new Runnable()
    {    
         public void run(){
             System.out.println("java with time contradicts itself");
         }
    }

is an instance of an anonymous class that implements interface Runnable The left part Runnable watdaheck, watdaheck is a reference that refers to above object. Your code is same with below code:

class SubRunnable implements Runnable{
   public void run(){
       //do something
   }
}
Runnable r = new SubRunnable();

You should read more about anonymous class in Java. https://docs.oracle.com/javase/tutorial/java/javaOO/anonymousclasses.html

TaQuangTu
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1

Runnable is an interface. We use it with the "new" operator in order to create an anonymous class object whICH

Rishabh Ritweek
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