Introduction to Object-Oriented Programming

Object-Oriented Programming Introduction

• Object-oriented programming (OOP) focuses on creating objects that contain both data and methods.
• Procedural programming focuses on writing procedures or methods to manipulate data.

Object-Oriented Languages

• OOP languages commonly support concepts like Polymorphism, Inheritance, Encapsulation, Abstraction, Classes, Objects, Instances, Methods, and Message Passing.

Objects and Classes

• An object has states (characteristics) and behaviors (actions).
• A class is a template or blueprint defining the behavior and state of its objects.
• Objects are instances of a class.
  • Each object inherits all variables and methods from its class.
• Example: A "Car" class can have objects like "Mercedes," "Volvo," and "Toyota."

Objects in Programming Languages

• Real-world objects (cars, dogs, humans) have states (characteristics) and behaviors (actions).
• Software objects mirror this with states stored in fields and behaviors shown via methods.
• Method calls operate on the object's internal state and are the communication means between objects.

States and Behaviors

• The state of an object is its properties (data). Alternative terms: instance variables, fields, properties, variables, members.
• Behaviors are the actions an object can perform (methods, functions, procedures).

Variable Types in a Class

• Local variables: Declared and initialized within a method; destroyed when the method ends.
• Instance variables: Belong to a specific object; initialized when the object is created. Accessed from within any method of the class containing it.
• Class variables: Belong to the class itself (not a specific object), declared with the "static" keyword. Accessed directly via the class name rather than an object instance.

Constructors

• Constructors are special methods called when a new object is created from a class.
• They initialize the new object's state.
• Each class has at least one constructor.
• Constructors have the same name as the class. A class can have multiple constructors.

Basic Syntax

• OOP code uses proper casing for identifiers. This means that Java, C# naming conventions are case-sensitive.
• Variables - camel case (use lowercase for the first word)
• Class Names - upper camel (use uppercase for every first character of each word)
• Method names - camel case (start with a lowercase letter).

Creating an Object

• Create an Object from a class in three steps:
  • Declare a variable of the class type
  • Instantiate the object using the 'new' keyword
  • Initialize the object by calling a constructor.
• Use the format [Object type] [variable name] = new [Constructor]();

UML

• UML (Unified Modeling Language) diagrams visually represent classes and their relationships.
• A UML diagram of a class can show the states (data) and behaviors (actions) of that class graphically.
• Use symbols like - for private access modifiers, and + for public access.

Classes (Sample Code)

• Classes are blueprints for creating objects.
• A class definition essentially creates all variables, actions, and properties for an object.
• A class can include instance variables, local variables, class variables, and methods

This quiz explores the fundamentals of object-oriented programming (OOP), including its core principles such as classes, objects, inheritance, and polymorphism. You'll learn how OOP differs from procedural programming and how it models real-world entities through software objects. Test your understanding of key concepts and terminology in OOP.