Question

I have 3 classes. They have all similar integers, methods etc…

class Country{

      int a,b;
public:
      Country();
      void doSomething();
      :
      :
}

class Military : public Country {
public:
      Power();
      void doAnother();
      void doAnother2();
      :
      :
}

class Technology : public Military{
public:
      Technology();
      void doAnother3();
      :
      :
}

Assume that this inheritance suits my solution. But as you see, when i create Military from Country, there is not a relation between them logically. I mean, military is not a country. Also for Technology from country, the problem is same. Technology is not a Military nor Country.

Anyway, that solution is okay for me, it shortens my code, but if i do this, do i betray Object Oriented Programming Philosophy? Is it a contradicton?

Answer 1

Yes, it’s against OOP. You relationships are has-a, not is-a.

You should use composition instead of inheritance for this.

class Country{
      Military m;  //Country has-a military
      int a,b;
public:
      Country();
      void doSomething();
}

class Military{
      Technology t; //Military has-a technology
public:
      Military();
      void doAnother();
      void doAnother2();
}

class Technology{
public:
      Technology();
      void doAnother3();
}