Why does the code can instantiate a java interface

Question

I understood that java interface cannot be instantiated. However, the below code looks like it instantiated an interface ? I'm trying to understand the code.

interface I{
    int a();
    int b();
}

public class C {
    public static void main(String [] arg){
    I i=(new I(){
        public int a(){return 1;}
        public int b(){return 2;}
    });
    assert i.a()==1 && i.b()==2;
    }
}

It instantiated an anonymous class that provides implementations of all the the methods of the interface — Mad Physicist, Jun 22 '22 at 04:52
https://stackoverflow.com/questions/355167/how-are-anonymous-inner-classes-used-in-java — Arun Sudhakaran, Jun 22 '22 at 09:16

score 2 · Accepted Answer · answered Jun 22 '22 at 04:55

An interface is like an all-abstract class, but that unambiguously supports multiple inheritance. You can instantiate any child of it that implements all the abstract methods.

The code you are asking about is creating an anonymous class that provides an implementation of all the abstract methods. Since the class is anonymous, the type of its instance can is most specifically given as I. Given that it's anonymous, that's also the only aspect of it you care about.

Why does the code can instantiate a java interface

1 Answers1