1. Lecture 14- Abstract Classes
Professor Adams

2. Rules for Abstract Classes
An abstract class can not be instantiated
An abstract class can’t have instances
A class that can have have instances is said to be concrete
An abstract class provides a prototype for other classes to follow

3. Subclasses of an Abstract Class
will inherit the variables and methods of the abstract class
will have the same basic characteristics
are free to redefine variables and methods and add new ones
must override any abstract methods of its parent.

4. Abstract Classes generally contain at least one abstract method
are not required by the compiler to be declared abstract – but we require it
are any classes containing at least one abstract method
can contain non-abstract methods

5. Abstract Methods have the word abstract in their declaration
do not have a body
end their declarations with a semi-colon
must be overriden in children of containing class
are generally methods whose bodies will change from one subclass to another

6. Standard UML Notation + public - private # protected {abstract}
top compartment – class name
middle compartment – class attributes
name : type
bottom compartment – class methods
returnType name (parameterList types)

7. Some Lewis & Loftus slides
Abstract Classes
Some Lewis & Loftus slides

8. Abstract Classes
An abstract class is a placeholder in a class hierarchy that represents a generic concept
An abstract class cannot be instantiated
We use the modifier abstract on the class header to declare a class as abstract:
public abstract class Whatever {
// contents }

9. Abstract Classes
An abstract class often contains abstract methods with no definitions
the abstract modifier must be applied to each abstract method
An abstract class typically contains non-abstract methods (with bodies)
A class declared as abstract does not need to contain abstract methods

10. Abstract Classes
The child of an abstract class must override the abstract methods of the parent, or it too will be considered abstract
An abstract method cannot be defined as final (because it must be overridden) or static (because it has no definition yet)
The use of abstract classes is a design decision – it helps us establish common elements in a class that is too general to instantiate

11. Indirect Use of Members - Inheritance
An inherited member can be referenced directly by name in the child class, as if it were declared in the child class
But even if a method or variable is not inherited by a child, it can still be accessed indirectly through parent methods
See FoodAnalyzer.java (page 459)
See FoodItem.java(page 460)
See Pizza.java (page 461)