Is it a good design ?

Question

Hello,
I have the following problem:
I have a base class, let's say class Base and 4 children of Base, let's say A, B, C, D. Each of them extends Base. In the Base class I made 4 "fake" - not implemented - methods, let's say k1, k2, k3, k4. Now the design problem/question: A class only uses k1 method, class B uses k1, k2, class C uses k1, k2, k3, class D uses all 4 methods. The reason why all 4 methods are in Base class is that I want to create an array of type Base and then initialize this array with either A objects, or B or C or D ( polymorphism thing :) ). If it's a bad design then how else would you make it ?
If you didn't get what I wrote, ask for more details :)
Regards

Answer 1

Here is how I did it:
I made four Interfaces : A, B extends A, C extends B and D extends C.
A has only k1() method, B has k2(), C has k3() and D has k4().
Implementations of these functions are different in every class.
I have also 4 classes: Aclass implements A, Bclass implements B etc.
Now I want to do the following thing:
Type[ ] arr = new Type[N];
if (....) {
   for( int i = 0; i < N; i++)
      arr[i] = new Aclass();
if (....) {
   for( int i = 0; i < N; i++)
      arr[i] = new Bclass();
if (....) {
   for( int i = 0; i < N; i++)
      arr[i] = new Cclass();
if (....) {
   for( int i = 0; i < N; i++)
      arr[i] = new Dclass();
}Question: what should be the type of "Type", so the program could compile ? If someone has any idea how else this can be solved, feel free to post :)
Regards