L2: Why Object-Oriented Programming (OOP) in Java

Overview

Object-Oriented Programming (OOP) is a programming paradigm that organizes software design around objects, which can represent real-world entities. Java uses OOP to make code more modular, reusable, and easier to maintain.

Key Concepts of OOP in Java

1. Classes and Objects:

   • A class is a blueprint for creating objects. It defines the attributes (variables) and behaviors (methods) that the objects created from the class will have.

   • An object is an instance of a class. Each object has its own set of attributes and can perform actions defined by its methods.

   • Example:

     public class Car {
         // Attributes
         String color;
         int speed;
     
         // Constructor
         public Car(String color, int speed) {
             this.color = color;
             this.speed = speed;
         }
     
         // Method
         public void accelerate() {
             speed += 10;
         }
     }
     
     public class Main {
         public static void main(String[] args) {
             // Creating an object
             Car myCar = new Car("Red", 0);
             myCar.accelerate();
         }
     }

2. Why OOP?

   • OOP allows breaking down complex problems into smaller, manageable pieces.
   • It improves code reusability by using classes as templates.
   • Makes it easier to maintain and modify code since each part (class) can be updated independently.

Identifiers in Java

• Identifiers are names used for classes, methods, variables, etc. They must follow certain rules:
  • Can contain letters, digits, underscores (_), and dollar signs ($).
  • Cannot start with a digit or use reserved keywords (e.g., int, class).
  • They are case sensitive.

Declaring and Using Variables

1. Variables: Hold data that can be used and manipulated within the program. Java is statically-typed, which means you must declare the type of a variable when creating it:

   int age = 25;
   String name = "Alice";
   • The type of the variable must match the type of value assigned to it.

2. Assignment: The = operator is used to assign values to variables.

3. Literals: A literal in Java is a fixed, specific value directly represented in the source code. It is a constant value that you assign to a variable or use in expressions. Since literals are not variables, their values are explicitly written and not meant to change during program execution.

Designing a Class with Attributes and Behaviors

• A class defines attributes using variables and behaviors using methods. Each object created from the class will have its own copy of the attributes:

  public class Dog {
      String breed;
      int age;
  
      public void bark() {
          System.out.println("Woof!");
      }
  }

• Creating and manipulating objects from a class:

  Dog myDog = new Dog();
  myDog.bark();

Benefits of OOP in Java

• Encapsulation: Bundles data (attributes) and code (methods) into a single unit (class).
• Modularity: Breaks down code into reusable parts, making it easier to update and maintain.
• Code Reusability: Classes can be used as templates for creating multiple objects with similar structures.