Why can't I define a static method in a Java interface?

Question

EDIT: As of Java 8, static methods are now allowed in interfaces.

Here\'s the example:

public interface IXMLizable         


        

Answer 1

I think java does not have static interface methods because you do not need them. You may think you do, but... How would you use them? If you want to call them like

MyImplClass.myMethod()

then you do not need to declare it in the interface. If you want to call them like

myInstance.myMethod()

then it should not be static. If you are actually going to use first way, but just want to enforce each implementation to have such static method, then it is really a coding convention, not a contract between instance that implements an interface and calling code.

Interfaces allow you to define contract between instance of class that implement the interface and calling code. And java helps you to be sure that this contract is not violated, so you can rely on it and don't worry what class implements this contract, just "someone who signed a contract" is enough. In case of static interfaces your code

MyImplClass.myMethod()

does not rely on the fact that each interface implementation has this method, so you do not need java to help you to be sure with it.