Generic Interface mess

generics, interface, java

Solution

1 Add generic to ICountable

public interface ICountable<T> extends IAddable<T>, Cloneable, Serializable {}

2 Specify generic in implementation

public class BaseCounter implements ICountable<BaseCounter> {
    @Override
    public BaseCounter add(BaseCounter other) {
        // TODO Auto-generated method stub
        return null;
    }
}

Problem

I am trying to encapsulate 3 interfaces in one (`ICountable`) and make concrete class implement this encapsulating interface. ``ICountable` code: ``` public interface ICountable extends IAddable, Cloneable, Serializable {} ``` `Addable` interface definition is: ``` public interface IAddable<T> { T add(T other); } ``` now when I am trying to implement `ICountable` in the concrete class (`BaseCounter`) I am getting the error that not all methods are implemented (complaining on `add` method). I fail to understand why. The `BaseCounter` code is as follows: ``` public class BaseCounter implements ICountable { @Override public BaseCounter add(BaseCounter other) { // TODO Auto-generated method stub return null; } } ``` Change `add` method signature to ``` public ICountable add(ICountable other) ``` fixes the situation. However, what I wanted originally, was to make one interface (`ICountable`) that extends 3 others (2 markers and 1 interface that describes the ability of the implementing class to perform `add` on the object of the same type). What I need to change in order to make `add` method implementation in `BaseCounter` look like this: ``` public BaseCounter add(BaseCounter other) ``` I would appreciate your suggestions.

Original source