More on Inheritance

Objectives

Notes

• A new access specifier
  • protected is somewhere between private and public.
    • It is used exclusively for inheritance.
    • A class instance has access to everything
    • A derived class has :
      • Full access to anything declared public
      • Full access to anything declared protected
      • No access to anything declared private
    • A non-related class has access to public and nothing else.
  • Protected is intended for
    • Utility members that derived members can use.
  • But since anyone can derive a class from your class (unless you use final), protected members are essentially public members.
  • And protected tends to break encapsulation, but that is big time OO theory.
  • The literature is mixed about protected
    • It is there so use it
    • It is bad, don't use it.
  • I tend to believe the later.
• final
  • Along with protected comes final
    • this is a specifier.
    • It follows the class name

    • class FighterT final : public PlayerT { 

• More on Virtual
  • As we said before, virtual marks a function as one that can be replaced in derived classes.
  • If virtual is not provided in a parent class, the function is not replaced, but hidden.
  • Look at PlayerT
    • Class() is declared in both the parent and derived class
    • But it is not marked virtual
    • So the derived class' Class() function hides the base class' Class() function.
    • And the derived class is NOT allowed to mark this as override
  • Virtual functions are intended to enforce an interface.
    • Ie derived classes can replace this, but all derived classes have one of these.
  • virtual only needs to be marked once
  • But it can be marked multiple times, ie in derived classes.
  • You only mark virtual in the .h file or .cpp file
  • I prefer the .h file.
• Sometimes you don't know how to deal with a function in a base class.
  • So you mark declare it an mark it as virtual to force it's creation in derived classes.
  • In addition you set it equal to 0

  • virtual void LevelUp() = 0; 

  • This creates a pure virtual function
  • Classes with pure virtual functions can not be instantiated.
  • Derived classes MUST implement these functions.
  • We will discuss virtual classes and pure virtual functions more later.
• Take a look at PlayerT.h, PlayerT.cpp and playerTest.cpp