Java OOP (Object-Oriented Programming)

Welcome to The Coding College! In this tutorial, we’ll explore Object-Oriented Programming (OOP) in Java, which is the foundation of modern software design. OOP helps developers create reusable, scalable, and maintainable applications.

What is OOP?

Object-Oriented Programming (OOP) is a programming paradigm based on the concept of “objects.” These objects encapsulate data (fields or attributes) and behavior (methods) to model real-world entities and interactions.

Core Principles of OOP

Java’s OOP is built on four key principles:

1. Encapsulation
   • Bundling data and methods into a single unit (class).
   • Protects data by restricting direct access.
2. Inheritance
   • Enables a class to inherit properties and methods from another class.
   • Promotes code reuse.
3. Polymorphism
   • Allows one interface to be used for different data types.
   • Achieved through method overriding and overloading.
4. Abstraction
   • Hides implementation details and only exposes essential features.
   • Achieved through abstract classes and interfaces.

Java OOP Terminologies

Example: Basic OOP Structure

Here’s a simple example that demonstrates OOP concepts in Java:

// Class definition
class Car {
    // Attributes
    String brand;
    String model;
    int year;

    // Constructor
    public Car(String brand, String model, int year) {
        this.brand = brand;
        this.model = model;
        this.year = year;
    }

    // Method
    public void displayInfo() {
        System.out.println("Car: " + brand + " " + model + " (" + year + ")");
    }
}

// Main class
public class Main {
    public static void main(String[] args) {
        // Creating an object
        Car car1 = new Car("Toyota", "Corolla", 2020);
        car1.displayInfo();
    }
}

Detailed Explanation

1. Class

A class is a template that defines the structure and behavior of an object.

class Car {
    String brand;
    String model;
    int year;
}

2. Object

An object is an instance of a class, created using the new keyword.

Car car1 = new Car("Toyota", "Corolla", 2020);

3. Constructor

A constructor initializes the object’s attributes when it is created.

public Car(String brand, String model, int year) {
    this.brand = brand;
    this.model = model;
    this.year = year;
}

4. Method

Methods define the behavior or actions of a class.

public void displayInfo() {
    System.out.println("Car: " + brand + " " + model + " (" + year + ")");
}

OOP Features in Depth

1. Encapsulation

Encapsulation restricts direct access to fields and allows controlled access using methods.

class Employee {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

2. Inheritance

Inheritance allows a class to acquire properties of another class.

class Animal {
    void eat() {
        System.out.println("This animal eats food.");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("The dog barks.");
    }
}

3. Polymorphism

Polymorphism allows a method to have different implementations.

class Animal {
    void sound() {
        System.out.println("This animal makes a sound.");
    }
}

class Dog extends Animal {
    @Override
    void sound() {
        System.out.println("The dog barks.");
    }
}

4. Abstraction

Abstraction hides complex details and shows only relevant information.

abstract class Shape {
    abstract void draw();
}

class Circle extends Shape {
    void draw() {
        System.out.println("Drawing a Circle.");
    }
}

Benefits of Java OOP

• Modularity: Code is organized into classes and objects.
• Reusability: Inheritance and polymorphism allow code reuse.
• Scalability: Objects can be easily modified without affecting the entire application.
• Security: Encapsulation protects data integrity.

Practice Problems

1. Create a BankAccount class with methods for deposit and withdrawal.
2. Build a class hierarchy for different types of vehicles.
3. Implement a polymorphic example using animals and their unique sounds.

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