1. Abstract Classes
Page

2. Page 198 Animal Inheritance Tree Good basis for the structure
Page 199 – New wolf; New Hippo from Animal class.
Can we create a new animal object from the animal class????

3. Page 200 What does a new Animal () object look like??
What would the instance variables be?
Some classes just should NOT be instantiated
Certain classes are created ONLY to be SuperClasses;
ONLY to be inherited from
There is a simple way to prevent a class from being instantiated

4. Abstract Marking the class as “abstract”
Abstract class Canine extends Animal
When designing your inheritance structure, you must decide which classes are abstract and which are concrete.
Concrete classes are those that are specific enough to be instantiated.
A concrete class means it’s OK to make objects of that type

5. Abstract – cont’d
An abstract class has virtually no use, no value, no purpose in life, unless it is extended
With an abstract class, the guys doing the work at runtime are instances of a subclass of your abstract class.
Look at Java API for examples - JComponent

6. Page 202 Look at illustration – top of page 202. Abstract Methods
You can mark methods abstract, too
An abstract class means the class must be extended
An abstract method means the method must be overridden.
An abstract method has no body. End with ;

7. Abstract Methods – cont’d
If you declare an abstract method, you MUST mark the class abstract as well. You can’t have an abstract method in a non-abstract class.
You MUST implement all abstract methods
Implementing an abstract method is just like overriding a method
Abstract methods – no body – exist only for polymorphism
First concrete class in the inheritance tree must implement all abstract methods.