README.md

Inheritance in Object-Oriented Programming (OOP)

Introduction

Inheritance is one of the core principles of Object-Oriented Programming (OOP). It allows a class (subclass or child class or derived class) to acquire the properties and behaviors of another class (superclass or parent class or base class). This promotes code reuse, scalability, and maintainability.

What is Inheritance?

Inheritance is a mechanism where a child class derives properties and behaviors from a parent class. The child class can:

• Use the fields and methods of the parent class
• Override parent class methods to provide a specific implementation
• Add its own additional properties and methods

Key Benefits of Inheritance

• Code Reusability: Avoids code duplication by reusing fields and methods of the parent class.
• Improves Maintainability: Reduces redundancy, making code easier to manage.
• Enhances Extensibility: New functionality can be added easily without modifying existing code.

---

How to Implement Inheritance in Java

Step 1: Create a Parent Class

The parent class contains common fields and methods.

// Parent class
public class Animal {
    String name;

    void eat() {
        System.out.println(name + " is eating...");
    }
}

Step 2: Create a Child Class using extends

The child class inherits the properties and methods of the parent class.

// Child class
public class Dog extends Animal {
    void bark() {
        System.out.println(name + " is barking...");
    }
}

Step 3: Use the Child Class

Now, let's create an object and use the inherited methods.

public class Main {
    public static void main(String[] args) {
        Dog myDog = new Dog();
        myDog.name = "Buddy";
        myDog.eat(); // Inherited from Animal class
        myDog.bark(); // Defined in Dog class
    }
}

Output:

Buddy is eating...
Buddy is barking...

---

Types of Inheritance in Java

Java supports different types of inheritance:

1. Single Inheritance

A subclass inherits from one superclass.

class Parent {
    void show() {
        System.out.println("This is the parent class");
    }
}

class Child extends Parent {
    void display() {
        System.out.println("This is the child class");
    }
}

2. Multilevel Inheritance

A subclass inherits from another subclass, forming a chain.

class Grandparent {
    void show() {
        System.out.println("Grandparent class");
    }
}

class Parent extends Grandparent {
    void display() {
        System.out.println("Parent class");
    }
}

class Child extends Parent {
    void print() {
        System.out.println("Child class");
    }
}

3. Hierarchical Inheritance

A single parent class has multiple child classes.

class Parent {
    void show() {
        System.out.println("Parent class");
    }
}

class Child1 extends Parent {
    void display() {
        System.out.println("Child1 class");
    }
}

class Child2 extends Parent {
    void print() {
        System.out.println("Child2 class");
    }
}

Note: Java does not support multiple inheritance (i.e., a child class inheriting from multiple parents) due to ambiguity problems.

---

Method Overriding in Inheritance

Method overriding allows a child class to redefine a method from the parent class.

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

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

Usage

public class Main {
    public static void main(String[] args) {
        Animal myAnimal = new Dog(); // Polymorphism
        myAnimal.makeSound();
    }
}

Output:

Dog barks

---

The super Keyword in Inheritance

The super keyword is used to refer to the parent class. It helps to:

1. Call the parent class constructor.
2. Access the parent class methods.
3. Access the parent class fields.

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

class Dog extends Animal {
    Dog() {
        super(); // Calls the parent class constructor
        System.out.println("Dog Constructor");
    }
    void makeSound() {
        super.makeSound(); // Calls parent method
        System.out.println("Dog barks");
    }
}

Usage

public class Main {
    public static void main(String[] args) {
        Dog myDog = new Dog();
        myDog.makeSound();
    }
}

Output:

Animal Constructor
Dog Constructor
Animal makes a sound
Dog barks