This document discusses specialization and inheritance in object-oriented programming. It explains that specialized classes inherit properties and methods from a parent or base class, and that inheritance allows for code reuse by permitting new classes to derive from existing classes without reimplementing their functionality. The document also covers protected access, using the super keyword to call parent constructors, polymorphism which allows specialized objects to be treated as general types, and abstract base classes which define common properties for derived classes without being instantiated themselves.

1. Specialization and
Inheritance
Chapter 8

2. 8
Specialization
Specialized classes inherit the
properties and methods of the
parent or base class.
A dog is a mammal
Hair
Live birth
A car is a vehicle
Wheels
Engine
Transports people
A Button is a Control

3. 8
Inheritance
Specialization is implemented in Java
through inheritance. The extends
keyword is used to implement this
relationship between classes.
class Dog extends (specializes)
Mammal
Mammal is the base class (superclass)
Dog is the derived class (subclass)

4. 8
Code Reuse with Inheritance
Inheritance permits easy reuse of
existing code.
A DeadBall class can be derived from a
Ball class.
Do not have to recode Ball
characteristics in DeadBall class

5. 8
Protected Access
private fields are inaccessible to
outside classes (including derived
classes).
protected fields are accessible to
derived classes, but not to outside
classes.

6. 8
Using super
The super keyword invokes the base
class’s constructor
Must be called from constructor of
derived class
Must be first statement within constructor

7. 8
More Rules forUsing super
Call must match the signature of a valid
signature in the base class
Implicitly called in the constructor if
omitted, so the base class must have a
default constructor
If derived class does not define a
constructor, the compiler provides one
and calls super automatically

8. 8
Polymorphism
An object can take many forms.
Method overloading is one type of
polymorphism.
Object polymorphism treats specialized
objects as if they are instances of a more
general type.

9. 8
Object Polymorphism
A method expecting a Car object can only
accept Car objects
A method expecting Vehicle objects can
accept any object derived from the
Vehicle class
Car
Truck
Bus

10. 8
Factoring to the Base Class
Factor common characteristics of
multiple classes up into a base class.
HWall and VWall classes have similar
characteristics and methods.
Factor commonalities to a Wall class
Override some methods to specialize the
HWall and VWall classes

11. 8
Abstract Base Classes
The classes describe what all derived
classes have in common.
Not instantiated (causes an exception)
Use the abstract keyword when defining
abstract base classes and methods

12. 8
Abstract Methods
Abstract methods are not implemented.
Derived classes must provide method
implementation.