Object Oriented Programming

Question 1

Object

Answer 1

• “a location in memory having a valve and reference by an identifier”
• have state (data) and behaviours (methods)

Question 2

Class and how to define

Answer 2

• template for an object

To Define:
- class name
- state: attributes (defined by variables)
- behaviours: actions of objects (defined by methods)

Question 3

Variables and two types of variables

Answer 3

• variables define state in a class - store data, fields, attributes

Types of Variables
- Instance - each object has its own copy of instance variables in the class
- Class - declared with keyword static, only one copy of a class variable is maintained for all objects to refer to

Question 4

Methods in a Class

Answer 4

• Accessor - Used to determine value of a variable (getter method)
• Modifier - used to change the value of a variable (setter method)
• Helper - called from within a class by other methods

Question 5

Constructors

Answer 5

• used to create an instance of an object
• have same name as the class
• a class can have more than one constructor (method overloading)
• used once per object - only to create or instantiate an object

Question 6

Inheritance

Answer 6

• class that is derived from another class inherits state and behaviours from that other class
• subclass (or child) automatically takes on all behaviors and attributes of its base class (parent)
• base class defines all the common features , subclasses inherit common feature
• Single Inheritance - you can only extend one class

Question 7

Subclass Initialization

Answer 7

• to initialize a subclass - must ensure we initialize all the state attributes that were inherited for super class
• in a default constructor we can invoke the superclass constructor by using keyword: super