1. CSC 205 Java Programming II
Inheritance

2. Topics What is Inheritance? Subclassing in Java
When not to use inheritance?
Overriding

3. Hierarchy Hierarchy is a ranking or ordering of abstractions
Two most important hierarchies
The “part-of” relationship, or aggregation
The “is-a” relationship , or inheritance
Inheritance, also known as subclassing
Single inheritance: the only legal way in Java
Multiple inheritance: supported in C++

4. Hierarchy: “is-a” relationship

5. Illustrating Inheritance
Account
specialization
generalization
SavingsAccount
CheckingAccount

6. Subclassing in Java A subclass SavingsAccount:
public class SavingsAccount extends Account {
private double interestRate;
public double getInterestRate() {
return interestRate; }
public void setInterestRate(double rate) {
interestRate = rate;

7. Writing a Subclass A SavingsAccount object will contain two variables:
balance, and
interestRate
Inherited from
Account

8. Writing a Subclass
Methods that can be applied to SavingsAccount objects:
getInterestRate
setInterestRate
deposit (inherited)
withdraw (inherited)
getBalance (inherited)
close (inherited)

9. When Not to Use Inheritance?
Inheritance is one from many kinds of relationships among classes
Don’t define an Account class by extending a Money class just because they are related
Other relationships are available
Aggregation: the “has-a” relationship
Dependency: the “use” relationship

10. Hierarchy: “part-of” relationship

11. Aggregation & Composition
University
aggregation
composition
Student
Department

12. The protected Access Modifier
Four levels of accessibility for class members
public
protected
(package or default)
private
The protected modifier allows for a subclass to access a member in its superclass

13. Overriding
A subclass can replace some of its inherited behavior by overriding
The toString() method
Although a class method may not be overridden, it may be hidden