Introduction

• Inheritance
  • Software reusability
  • Create new class from existing class
    • Absorb existing class's data and behaviors
    • Enhance with new capabilities
  • Derived class inherits from base class
    • Derived class
      • More specialized group of objects
      • Behaviors inherited from base class; can customize
      • Additional behaviors
• Class hierarchy
  • Direct base class; inherited explicitly (one level up hierarchy)
  • Indirect base class; inherited two or more levels up hierarchy
  • Single inheritance; inherits from one base class
  • Multiple inheritance; Inherits from multiple base classes (Base classes possibly unrelated ); Chapter 22
• Three types of inheritance
  • public
    • Every object of derived class also object of base class
      • Base-class objects not objects of derived classes
      • Example: All cars vehicles, but not all vehicles cars
    • Can access non-private members of base class
      • Derived class can effect change to private base-class members
      • Through inherited non-private member functions
  • private
    • Alternative to composition
    • Chapter 17
  • protected
    • Rarely used
• Abstraction
  • Focus on commonalities among objects in system; "is-a" vs. "has-a"
  • "is-a"
    • Inheritance
    • Derived class object treated as base class object
    • Example: Car is a vehicle; Vehicle properties/behaviors also car properties/behaviors
  • "has-a"
    • Composition
    • Object contains one or more objects of other classes as members
    • Example: Car has a steering wheel