Inheritance in Java

The word 'inherit' means receive.

Imagine a parent and a child, how a child's genetical nature, color would be?

The child's characteristics(color,height) will depend upon the child's parents. Right?

We can say the above as the child inherits the properties of a parent.

Imagine child as a class and parent as a another class. If we create methods and variables for parent class, we can use same methods and variables in the child class without re-writing methods. i.e reusability of codes. This is called as inheritance.

Inheritance is the concept of deriving a parent class property from a child class.

Here derived class - sub-class and parent class - super class

To derive a class from parent-class, we use extends

General Syntax

class subclass_name extends superclass_name{

//body of the class

}


Types of Inheritance

Single Inheritance

When a child class inherits a parent class, it is known Single inheritance.

Example

class MotorCycle{

MotorCycle(){

System.out.println("It has two wheels");

}

void engine(){

System.out.println("Petrol Engine");

}

}

class RoyalEnfield extends MotorCycle{

void mileage(){

System.out.println("It has 20 km mileage.");

}

public static void main(String args[]){

RoyalEnfield re=new RoyalEnfield();

re.mileage();

re.engine();

}

}

Try In Editor

Output

It has two wheels

It has 20 kms mileage.

Petrol Engine

Order of execution

At first, Parent's constructor i.e. MotorCycle() in above example is executed.

Next, Child's constructor i.e.RoyalEnfield()

Then as per the call of methods and variables i.e. re.mileage().


Multi-level Inheritance

Inheriting a parent class by a child and the child again is inherited by a grand-child is known Multi-level inheritance.

Example

class Vehicle{

Vehicle(){

System.out.println("It is used for transporting people and goods.");

}

}

class FourWheeler extends Vehicle{

FourWheeler(){

System.out.println("It contains four wheels.");

}

}

class Car extends FourWheeler{

Car(){

System.out.println("It can carry only small number of people.");

}

public static void main(String args[]){

System.out.println("Properties and usage of a car are ");

Car car=new Car();

}

}

Try In Editor

Output

Properties and usage of a car are

It is used for transporting people and goods.

It contains four wheels.

It can carry only small number of people.


Hierarchial Inheritance

Inheriting a parent class by many childs is known Hierarchial inheritance.

Example

class MotorCycle{

MotorCycle(){

System.out.println("It has two wheels");

}

void engine(){

System.out.println("Petrol Engine");

}

}

class RoyalEnfield extends MotorCycle{

void mileage(){

System.out.println("It has 20 km mileage.");

}

}

class Yamaha extends MotorCycle{

void mileage(){

System.out.println("It has 30 km mileage.");

}

public static void main(String args[]){

System.out.println("About RoyalEnfield :");

RoyalEnfield re=new RoyalEnfield();

re.mileage();

re.engine();

System.out.println("About Yamaha :");

Yamaha yh=new Yamaha();

yh.mileage();

yh.engine();

}

}

Try In Editor

Output

About RoyalEnfield :

It has two wheels

It has 20 kms mileage.

Petrol Engine

About Yamaha :

It has two wheels

It has 30 kms mileage.

Petrol Engine