Inheritance in Java

Inheritance is a process by which one class acquires properties (data members and methods) of another class. It is very essential feature of object oriented programming. Most important aspect of inheritance is reusability. We have to only unique features in derived class, other common features is extended from the base class. 

Derived Class: The class that inherits the properties (data members and methods) of base class.

Base Class: The class whose properties (data members and methods) are extended by derived class.

Uses of Java Inheritance

- Code Reusability

- Method overriding (runtime polymorphism)

- Save time for writing same code over and over.

Syntax of Java Inheritance

class Derivedclass-name extends Baseclass-name  
{  
   //data members and methods
}

The “extends” keyword is used for inheritance in java. The “extends” means increase the features.

Java Inheritance Example

In this example, Student class extends Person class. Person class has two data members and one parametrized constructor. Student class inherits the properties of person class. All students have a name, age and roll no. For storing name and age of students, data members of person class are used. And age of student is stored in data member of student class. In the Student class constructor, we call the Person class constructor using super keyword.

class Person
{
 String name; 
 int age;
 Person(String n, int a)
 {
  name = n;
  age = a;
 }
}
class Student extends Person
{
 int rollno;
 Student(String n, int a, int r)
 {
  super(n, a);
  rollno = r;
 }
 void showDetails()
 {
  System.out.println("Name : "+super.name);
  System.out.println("Age : "+super.age);
  System.out.println("Roll no : "+rollno);
 }
}
class Inheritance
{
 public static void main(String[] args) {
  Student s = new Student("John", 18, 30);
  s.showDetails();
 }
}

Output:

Name : John
Age : 18
Roll no : 30

Types of Inheritance in Java

Following are the types of inheritance supported by java.

Single Inheritance

Single Inheritance

In single inheritance, there is only one base class and derived. This type of inheritance is very simple and easy to understand.

Multilevel Inheritance

Multilevel Inheritance

In multilevel inheritance, derived inherits the properties of base class and further another class inherits properties of that derived class and so on. For example, class B inherits properties of class A and class C inherits properties of class B.

Hierarchical Inheritance

Hierarchical Inheritance

In hierarchical inheritance, multiple derived classes inherits the properties of single base class. For example, class B and class C inherits properties of class A.

Multiple Inheritance

Multiple Inheritance

Multiple inheritance cannot be achieved by class, it is only achieved by interfaces. In multiple inheritance, an interface inherits the properties of two or more two interfaces. For example, interface C inherits properties of interface A and B

Hybrid Inheritance

It is combination of more than one type of inheritance. For example, a combination of single and hierarchical inheritance.