Confusion about Thread [duplicate]

Answer 1

The trick used here is called anonymous classes. Basically, you are creating a object of a new anonymous class that implements Runnable.

The better example would be this:

Thread t = new Thread(new Runnable(){ 
   @Override
   public void run() {
       // Code here
   }
});

Answer 2

We can create a reference of an interface but not object

That's not true.

ClassA classa = new ClassA(); 

This will make a new instance for ClassA, while classa is the reference.

But how can we pass new Runnable() to the Thread constructor

Thread t = new Thread(new Runnable(){});

This will make an instance of a Thread, where t is the reference. The new Runnable(){} is called an anonymous class. Because an instance is created, the reference is passed to the constructor, but you can't refer to this one later in the code.

But with this line you should get a compile error. You have to override the run method.

Thread t = new Thread(new Runnable(){
    @Override
    public void run(){
    }
});