Inheritance in Java

What is Inheritance?

Inheritance is a fundamental concept in object-oriented programming (OOP). It allows one class to inherit the properties and behaviors of another class, creating a parent-child relationship between the classes.

How Does It Work?

In Java, you can create a base class (or parent class) with common features. Other classes, known as derived classes (or child classes), can inherit and use these features.

Why Use Inheritance?

Reusability: Use the same code in different places.
Organization: Group related features together.
Specialization: Create specialized versions of a class.

Commonly used Inheritance

1. Single Inheritance: A class inherits from one base class.

Single Inheritance Example:

Explanation:

public class Animal {

// This line defines a new class called ‘Animal’.
// A class is like a blueprint for creating objects with specific features and behaviors.

public void eat() {

// This line defines a method called ‘eat’ inside the ‘Animal’ class.
// A method is a block of code that performs a specific task.

System.out.println(“Animal is eating.”);

// This line prints the text “Animal is eating.” to the console.

public class Dog extends Animal {

// This line defines a new class called ‘Dog’ that inherits from the ‘Animal’ class by using the ‘extends’ keyword.
// Inheriting means ‘Dog’ will have all the features of ‘Animal’ plus its own features.

public void bark() {

// This line defines a method called ‘bark’ inside the ‘Dog’ class.
// The ‘bark’ method is specific to the ‘Dog’ class.

System.out.println(“Dog is barking.”);

// This line prints the text “Dog is barking.” to the console.

2. Hierarchical Inheritance: Multiple classes inherit from one base class

Hierarchical Inheritance Example:

public class Animal {
    public void eat() {
        System.out.println(“Animal is eating.”);
    }
}
public class Dog extends Animal {
    public void bark() {
        System.out.println(“Dog is barking.”);
    }
}
public class Cat extends Animal {
    public void meow() {
        System.out.println(“Cat is meowing.”);
    }
}

Explanation:

public class Animal {

// This line defines a new class called ‘Animal’.
// A class is like a blueprint for creating objects with specific features and behaviors.

public void eat() {

// This line defines a method called ‘eat’ inside the ‘Animal’ class.
// A method is a block of code that performs a specific task.

System.out.println(“Animal is eating.”);

// This line prints the text “Animal is eating.” to the console.

public class Dog extends Animal {

public void bark() {

// This line defines a method called ‘bark’ inside the ‘Dog’ class.
// The ‘bark’ method is specific to the ‘Dog’ class.

System.out.println(“Dog is barking.”);

// This line prints the text “Dog is barking.” to the console.

public class Cat extends Animal {

// This line defines a new class called ‘Cat’ that also inherits from the ‘Animal’ class by using the ‘extends’ keyword.
// This means ‘Cat’ will have all the features of ‘Animal’ plus its own features.

public void meow() {

// This line defines a method called ‘meow’ inside the ‘Cat’ class.
// The ‘meow’ method is specific to the ‘Cat’ class.

System.out.println(“Cat is meowing.”);

// This line prints the text “Cat is meowing.” to the console.

Multilevel Inheritance: A class inherits from a derived class.

Multilevel Inheritance Example:

public class Animal {
    public void eat() {
        System.out.println(“Animal is eating.”);
    }
}
public class Mammal extends Animal {
    public void breathe() {
        System.out.println(“Mammal is breathing.”);
    }
}
public class Dog extends Mammal {
    public void bark() {
        System.out.println(“Dog is barking.”);
    }
}

Explanation:

public class Animal {

// This line defines a new class called ‘Animal’.
// A class is like a blueprint for creating objects with specific features and behaviors.

public void eat() {

// This line defines a method called ‘eat’ inside the ‘Animal’ class.
// A method is a block of code that performs a specific task.

System.out.println(“Animal is eating.”);

// This line prints the text “Animal is eating.” to the console.

public class Mammal extends Animal {

// This line defines a new class called ‘Mammal’ that inherits from the ‘Animal’ class by using the ‘extends’ keyword.
// Inheriting means ‘Mammal’ will have all the features of ‘Animal’ plus its own features.

public void breathe() {

// This line defines a method called ‘breathe’ inside the ‘Mammal’ class.
// The ‘breathe’ method is specific to the ‘Mammal’ class.

System.out.println(“Mammal is breathing.”);

// This line prints the text “Mammal is breathing.” to the console.

public class Dog extends Mammal {

// This line defines a new class called ‘Dog’ that inherits from the ‘Mammal’ class by using the ‘extends’ keyword.
// Inheriting means ‘Dog’ will have all the features of ‘Mammal’ plus its own features.

public void bark() {

// This line defines a method called ‘bark’ inside the ‘Dog’ class.
// The ‘bark’ method is specific to the ‘Dog’ class.

System.out.println(“Dog is barking.”);

// This line prints the text “Dog is barking.” to the console.

Tasks:
1. Single Inheritance:
Create a base class Vehicle with a method start that prints “Vehicle started”. Derive a class Car from Vehicle and add a method drive that prints “Car is driving”. Create an object of Car in the main method, call the start and drive methods.

2. Hierarchical Inheritance:
Create a base class Person with a method walk that prints “Person is walking”. Derive two classes Student and Teacher from Person. Add a method study in Student that prints “Student is studying” and a method teach in Teacher that prints “Teacher is teaching”. Create objects of Student and Teacher in the main method and call their respective methods.

3. Multilevel Inheritance:
Create a base class ElectronicDevice with a method turnOn that prints “Device turned on”. Derive a class Computer from ElectronicDevice and add a method boot that prints “Computer is booting”. Further derive a class Laptop from Computer and add a method charge that prints “Laptop is charging”. Create an object of Laptop in the main method, call all methods.

4. Inheritance with Constructors:
Create a base class Building with a property address and a constructor to initialize this property. Derive a class House from Building and add a property numberOfRooms. Add a constructor to House that calls the base class constructor. Create an object of House in the main method and set all properties.