Inheritance Background and Design

• See page 130 in the book.
• As we have seen, inheritance is a mechanism for deriving new classes from existing classes.
  • Starting from a base class
  • We can produce derived classes
• We can
  • Add new members (data and methods)
  • Overwrite the implementation of methods.
  • Extend existing methods.
• The relationship between objects is often described as an is-a relationship.
  • In our example, A farm is a building.
• We will do this for multiple different buildings.
• In UML
  • An arrow from the derived class to the base class.
  • The arrow "point" is a hollow triangle.
  • 
• Right now, our example just hides the implementation of methods.
  • This is not the best.
  • And you can see at the end where it sort of "fails"
• We can make a class abstract by declaring at least one method pure virtual.
  • Virtual methods are methods that are intended to be replaced.
  • Pure virtual methods are methods without an implementation.
• Polymorphism is the ability to adopt different forms.
  • We have seen a primitive form of this.
  • Polymophism allows us to employ hierarchies very efficiently.