Inheritance in Java

Inheritance in java is a mechanism in which one object acquires all the properties and behaviors of parent object.
The idea behind inheritance in java is that you can create new classes that are built upon existing classes. When you inherit from an existing class, you can reuse methods and fields of parent class, and you can add new methods and fields also
Inheritance represents the IS-A relationship, also known as parent-child relationship.

Why use inheritance in java

  • For Method Overriding (so runtime polymorphism can be achieved)..
  • For Code Reusability.

    • Syntax:

    class Subclass-name extends Superclass-name  
 {  
    //methods and fields  
  }
    The extends keyword indicates that you are making a new class that derives from an existing class. The meaning of "extends" is to increase the functionality.
    In the terminology of Java, a class which is inherited is called parent or super class and the new class is called child or subclass.

    Example

    class Person  {  
float salary=80000.0f;  
  }  
class Servant extends Person {  
int bonus=10000.0f;  
public static void main(String args[]) {  
Servant S=new Servant();  
System.out.println("Servant salary is:"+S.salary);  
System.out.println("Bonus of Servant is:"+S.bonus);  
  }  
  }

    Output:

    Servant salary is:  80000
Bonus of Servant is: 10000

    Types of inheritance in java

    On the basis of class, there can be three types of inheritance in java: single, multilevel and hierarchical.
    In java programming, multiple and hybrid inheritance is supported through interface only

    Multiple inheritance is not supported in java through class.
    When a class extends multiple classes i.e. known as multiple inheritance

    Example:


    Single Inheritance

    Example:

    File: TestInheritance.java 
    class Person{  
void eat() {
System.out.println("person is eating");
  } }  
class Child extends Person {  
void walks() { 
System.out.println("Child is walking");
 } }  
class TestInheritance{  
public static void main(String args[]){  
Child c = new Child();  
c.walks();  
c.eat();  
 }}

    Output:

    Person is eating
Child is walking

    Multilevel Inheritance

    Example:

    File: TestInheritance1.java 
    class Person{  
void eat() {
System.out.println(" Person is eating");
 }  }  
class Child extends Person{  
void walks() {
System.out.println("Child is walking");
 }  }  
class BabyChild extends Child{  
void Laugh() { 
System.out.println("BabyChild is Laughing");
 }  }  
class TestInheritance1{  
public static void main(String args[]){  
BabyChild b=new BabyChild();  
b.Laugh();  
b.walks();  
b.eat();  
}}

    Output:

    Person is eating
Child is walking
BabyChild is Laughing

    Hierarchical Inheritance

    Example:

    file:TestInheritance2.java 
    class Person{  
void eat() {
System.out.println(" Person is eating");
 }  }  
class Child extends Person{  
void walks() {
System.out.println("Child is walking");
 }  }  
class BabyChild extends Child{  
void Laugh() { 
System.out.println("BabyChild is Laughing");
 }  }  
class TestInheritance1{  
public static void main(String args[]){  
BabyChild b=new BabyChild();  
b.Laugh();  
//b.walks(); //Comment here   
b.eat();  
}}

    Output:

    Person is eating
BabyChild is Laughing

    Why multiple inheritance is not supported in java?

    To reduce the complexity and simplify the language, multiple inheritance is not supported in java.
    Consider a scenario where A, B and C are three classes. The C class inherits A and B classes. If A and B classes have same method and you call it from child class object, there will be ambiguity to call method of A or B class.
    Since compile time errors are better than runtime errors, java renders compile time error if you inherit 2 classes. So whether you have same method or different.