Inheritance is an important concept of OOP(Object-Oriented Programming). It is the mechanism by which one class is allowed to inherit the features(fields and methods) of another class.
Inheritance represents the IS-A relationship which is
also known as a parent-child relationship.
Inheritance is used for code reusability.
The keyword used for inheritance is extends. The extends
keyword indicates that you are making a new class that derives from an
existing class.
syntax:
class Subclass-name extends Superclass-name
{
//methods and fields
}
In the terminology of Java, a class which is inherited is called a parent
or superclass, and the new class is called child or subclass.
Types of
Inheritance in Java
On the basis of class, there can be three types of inheritance in java:
single, multilevel and hierarchical.
1. Single Inheritance: In single inheritance, subclasses inherit the features of one superclass.
In the image below , class A serves as a base class for the derived class
B.
// Java program to illustrate the concept of single inheritance
import java.io.*;
import java.lang.*;
import java.util.*;
class one {
public void print_one()
{
System.out.println("one");
}
}
class two extends one {
public void print_two()
{ System.out.println("two"); }
}
// Driver class
public class Main {
public static void
main(String[] args)
{
two g = new
two();
g.print_one();
g.print_two();
}
}
2. Multilevel
Inheritance: In Multilevel Inheritance, a derived class will be
inheriting a base class and as well as the derived class also act as the base
class to other class. In the below image, class A serves as a base class for
the derived class B, which in turn serves as a base class for the derived class
C.
// Java program to illustrate the concept of Multilevel inheritance
import java.io.*;
import java.lang.*;
import java.util.*;
class one {
public void print_one()
{
System.out.println("one");
}
}
class two extends one {
public void print_two()
{ System.out.println("two"); }
}
class three extends two {
public void print_three()
{
System.out.println("three");
}
}
public class Main {
public static void
main(String[] args)
{
three g =
new three();
g.print_one();
g.print_two();
g.print_three();
}
}
3. Hierarchical
Inheritance: In Hierarchical Inheritance, one class serves as a
superclass (base class) for more than one subclass. In the below image, class A
serves as a base class for the derived class B, C and D.
// Java program to illustrate the concept of
Hierarchical inheritance
class A {
public
void print_A() { System.out.println("Class A"); }
}
class B extends A {
public
void print_B() { System.out.println("Class B"); }
}
class C extends A {
public
void print_C() { System.out.println("Class C"); }
}
public class Test {
public
static void main(String[] args)
{
B
obj_B = new B();
obj_B.print_A();
obj_B.print_B();
C
obj_C = new C();
obj_C.print_A();
obj_C.print_C();
}
}
Multiple
inheritance
To reduce the complexity and simplify the language,
multiple inheritance is not supported in java.
In Multiple inheritance, one class can have more
than one superclass and inherit features from all parent classes. In java
programming, multiple and hybrid inheritance is supported through interface
only.
// Java program to illustrate the
// concept of Multiple inheritance
import java.io.*;
import java.lang.*;
import java.util.*;
interface one {
public
void print_g();
}
interface two {
public
void print_for();
}
interface three extends one, two {
public
void print_g();
}
class child implements three {
public
void print_g()
{
System.out.println("multiple");
}
public
void print_in() { System.out.println("inheritance"); }
}
public class Main {
public
static void main(String[] args)
{
child
c = new child();
c.print_g();
c.print_in();
}
}
