Core Java - Object- Oriented Programming (OOP) Principles

8. Object- Oriented Programming (OOP) Principles

Object-Oriented Programming (OOP) is a programming paradigm that focuses on organizing code into reusable, self-contained objects. Java is an object-oriented language, and understanding OOP principles is fundamental to becoming a proficient Java developer. In this Core Java tutorial, we'll explore the core OOP principles in Java, along with detailed explanations and examples.

1. Classes and Objects:

• Class: A class is a blueprint or template for creating objects. It defines the structure and behavior of objects.

public class Car {
    String make;
    String model;
    int year;

    void startEngine() {
        System.out.println("Engine started.");
    }

    void stopEngine() {
        System.out.println("Engine stopped.");
    }
}

• Object: An object is an instance of a class. It represents a real-world entity and has its own state and behavior.

Car myCar = new Car();
myCar.make = "Toyota";
myCar.model = "Camry";
myCar.year = 2022;
myCar.startEngine();

2. Encapsulation:

Encapsulation is the practice of hiding the internal details of an object and providing a controlled interface for interacting with it. This is achieved through access modifiers like 'public', 'private', and 'protected'.

public class BankAccount {
    private double balance;

    public void deposit(double amount) {
        if (amount > 0) {
            balance += amount;
        }
    }

    public double getBalance() {
        return balance;
    }
}

In this example, the 'balance' variable is encapsulated by making it 'private', and access is provided through 'deposit' and 'getBalance' methods.

3. Inheritance:

Inheritance allows a class to inherit properties and behaviors from another class. In Java, you can create a new class based on an existing class (superclass) to reuse and extend its functionality.

class Animal {
    void eat() {
        System.out.println("Animal is eating.");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Dog is barking.");
    }
}

In this example, the  'Dog' class inherits the 'eat' method from the 'Animal' class and adds its own 'bark' method.

4. Polymorphism:

Polymorphism allows objects of different classes to be treated as objects of a common superclass. It enables flexibility in method invocation based on the actual object type.

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

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

class Square extends Shape {
    @Override
    void draw() {
        System.out.println("Drawing a square.");
    }
}

abstract class Shape {
    abstract void draw();
}

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

class Square extends Shape {
    @Override
    void draw() {
        System.out.println("Drawing a square.");
    }
}