Recap

Encapsulation

• Core principle of Object-Oriented Programming (OOP)
• Objects are instances of a class, and an object is a unit with its data (variables) and the methods that operate on that data
• Encapsulation restricts direct access to an object’s internal state and provides controlled access through well-defined methods

Encapsulation

• private instance variables (data hiding)
• Getters and Setters (controlled access)

Benefits: modularity, easier to test and maintain, data integrity and validation, flexibility in refactoring

Inheritance

Use keyword extends to extend a parent class and create a subclass

• subclass inherits instances and methods from super (parent) class
• subclass has a constructor obligation with parent class (parent constructor always runs)
• use super(params) in subclass constructor (needs to be first line) to satisfy parent class constructor requirements
• use super.method() or super.variableName to access public or protected members of parent class

A good parent class

careful use of privacy:

• public “how outsiders use my family”
• protected “provided to my children”
• private “I’ll handle this myself”

Gives structure and design to children

Designed with polymorphism in-mind

Polymorphism

• Method overloading – methods with same name but different signatures in the same class
• Method overriding – methods with the same name and signature in parent-child classes (we often override toString() and equals(Object obj))

Important syntax

instanceof – evaluates to true if and only if reference is a member of Type

variableName instanceOf Type

We use instanceof together with type casting

(SubClass) parClassVariableName

Converts a parent-class-reference (storing a child class) to a child-class reference (no actual conversion) – purpose is to call methods in subclass

Quiz 7

You have 10 minutes to complete the quiz.

Complete the body of three methods in subclass: StudentTicket constructor, setDiscount(double discount) with validation, and getPrice() (with calculated discount)