OOP (W1)

• Object Oriented Programming (OOP)


  A programming paradigm that focuses on the use of objects to represent and manipulate data
• OOP


  • Data is encapsulated within the objects
  • Objects are defined by their properties (attributes) & behaviors (methods)
  • Enables developers to write modular, reusable, and maintainable code
• Objects


  • Instances of a class which are created from a class in java or any other languages
  • They have states and behavior
  • Correspond to things found in the real world i.e. real entities
  • Called run-time entities of the world
• Instant variables


  Variables or data defined within a class
• Code


  Always contained in the methods
• Members of a class

  Methods & variables defined within a class
• OOP concepts defined in Java

  • Abstraction
  • Encapsulation
  • Inheritance
  • Polymorphism
• Abstraction


  • Represents simple things like objects, classes & variables as more complex underlying code and data
  • Lets you avoid repeating the same work multiple times
• Encapsulation


  • Practice of keeping fields within a class private, then providing access to those fields via public methods
  • Protective barrier that keeps the data and code safe within the class itself
• Inheritance


  • Lets programmers create new classes that share some of the attributes of existing classes
  • Lets us build on previous work without reinventing the wheel
• Polymorphism


  • Allows programmers to use the same word in Java to mean different things in different contexts
  • One form is method overloading, another is method overriding
• How Abstraction works


  Enables programmers to create complex systems by breaking them down into smaller, more manageable components
• Abstract keyword


  Non-modifier, used for classes and methods
• Abstract class


  Restricted class that cannot be used to create objects, must be inherited from another class
• Abstract method


  Can only be used in an abstract class, and does not have a body. The body is provided by the subclass.
• Data abstraction


  Process of hiding certain details and showing only essential information to the user
• Interfaces


  Collection of methods, used to define a set of behaviors that a class should implement
• How Encapsulation works

  Lets us reuse functionality without jeopardizing security
• Benefits of Encapsulation

  • Data hiding - protects data from unauthorized access and manipulation
  • Modularity - breaks down complex systems into smaller, more manageable components
  • Flexibility - allows changes to internal implementation without affecting external interface
• Access modifiers in Java

  • Public - variables and methods can be accessed from anywhere
  • Private - variables and methods can only be accessed within the class they are defined in
  • Protected - variables and methods can be accessed within the same class and its subclasses
• How Inheritance works

  1. Lets a new class adopt the properties of another

  2. The inheriting class is called a subclass or child class

  3. The original class is called the parent or superclass

  4. We use the keyword 'extends' to define a new class that inherits from an old class
• Benefits of Inheritance

  • Reusability - subclass can reuse code and functionality already defined in the superclass
  • Polymorphism - objects of different subclasses can be treated as objects of the same superclass
  • Flexibility - new features can be added to an existing class hierarchy without modifying existing code
• How Polymorphism works

  1. Uses a reference to a parent class to affect an object in the child class

  2. Examples include method overriding and method overloading
• Method overriding


  The child class can override a method of its parent class, allowing the same method to be used in different ways
• Method overloading


  A single method may perform different functions depending on the context in which it's called
• Benefits of Polymorphism

  • Flexibility - enables more flexible and adaptable code
  • Code reuse - promotes code reuse by allowing classes to inherit functionality
  • Simplification - enables the use of generic code that can handle different types of objects