Question

I have an interface A, for which I have to supply a few different implementations. However, those implementations share some helper methods, so I moved those methods to an abstract base class.

Interface A {     void doX(); }  abstract Class B implements A {     protected void commonY() {         // ...     }      @Override     public abstract void doX(); }  Class C extends B {     @Override     public void doX() {         // ...     } }  Class D extends B {     @Override     public void doX() {         // ...     } } 

My code works as expected, but I have a few questions:

• Should I declare the abstract Method doX() in Class B? Why (not)?

• Should I also explicitly declare ‘implements A’ on Class C and D? Why (not)?

Answer 1

I think it would be better to do it as follows:

Interface A {         void doX(); }  abstract Class B {         protected void commonY() {                 // ...         } }  Class C extends B implements A{          public void doX() {                 // ...         } }  Class D extends B implements A{          public void doX() {                 // ...         } } 

You shouldn’t mix the interface (signature of methods) with the implementation.