CSC 205 Java Programming II Inheritance

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

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++

Hierarchy: “is-a” relationship

Illustrating Inheritance Account specialization generalization SavingsAccount CheckingAccount

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;

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

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

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

Hierarchy: “part-of” relationship

Aggregation & Composition University aggregation composition Student Department

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

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