Java Interface-Implementation Pair [closed]

Answer 1

This is the approach I would take:

public interface MyInterface {

      MyInterface DEFAULT = new MyDefaultImplementation();

      public static class MyDefaultImplemenation implements MyInterface {
      }
 }

Of course, the MyDefaultImplementation may need to be private, or its own top level class, depending on what makes sense.

You can then have the following in your implementations:

 public class MyClass implements MyInterface {
        @Override
        public int someInterfaceMethod(String param) {
             return DEFAULT.someInterfaceMethod(param);
        }
  }

Its a bit more self-documenting, and ultimately more flexible, than a default implementation class that exists elsewhere but is not referenced by the interface. With this you can do things like just pass the default implementation as a method parameter when required (which you cannot do with the static methods).

Of course, the above only works if there is no state involved.