Why are interfaces in Java 8 allowed to have the main method?

Question

Why are interfaces allowed to have a main method in Java 8?

As stated in below code it works fine and produces output properly.

public interface Temp {     public static void main(String args[]){          System.out.println("Hello");     } } 

Currently it is behaving like a class and I have executed interface with main method.

Why do we need this?

Answer 1

Since Java 8, static methods are allowed in interfaces.

main() is a static method.

Hence, main() is allowed in interfaces.

We don't need this, since it wasn't allowed before, and yet we survived. But since static methods, by definition, are not bound to an instance of a class, but to the class itself, it makes sense to allow them in interfaces. It allows defining utility methods related to an interface (like the ones found in Collections, for example), in the interface itself, rather than a separate class).

There is no difference between class static methods and interface static methods.

Answer 2

I second the answer of @jb-nizet. There is no "desparate need" for this, but it removes an unnecessary restriction. E.g. one example is, that you can now declare a factory method within the interface:

 public interface SomeService {     public static SomeService getInstance() {      // e.g. resolve via service provider interface    }     ...   } 

Before Java 8 we needed always a separate factory class. One favorite example is the google app engine API.