INHERITANCE IN JAVA

The process of creating a class to reuse exiting class members using our class name or object is called inheritance. It can be defined as a process of obtaining one object property to another object. The concept of getting the properties of one class to another class is known as inheritance.

Super class – any class which is getting extended by another class is known as super class.

Sub class – any class which is extending another class is known as subclass.

We use inheritance for method overriding and for code reusability.

Syntax –

class Subclass extends Superclass

{

          ------

          ------

}

The extends keyword indicates that we are making a new class that derives from an existing class.

Example –

class Employee{

          float salary=40000;

}

public class Programmer extends Employee{

          int bonus = 10000;

          public static void main(String[] args) {

                   Programmer p = new Programmer();

                   System.out.println("Programmer salary is : "+p.salary);

                   System.out.println("Programmer bonus is : "+p.bonus);

          }

}

Output –

Programmer salary is : 40000.0

Programmer bonus is : 10000

Important points to be remembered with respect of inheritance –

• ·        Always super class objects are created from the subclass constructors. It is the subclass constructor which would be creating object of super class in association with the subclass object, by calling the super class constructor.
• ·        Sub class objects or objects of any classes can’t be created without creating super class objects.
• ·        Always the super class objects are created first and sub class objects are created last. 

Types of inheritance –

·        Single level

·        Multi level

·        Hierarchical

·        Hybrid

·        Multiple interface inheritance

Note – Java does not support multiple inheritance, but it provides alternative method to support multiple inheritance with interfaces.

1. Single level inheritance – If two classes or two interfaces or a class and interface participating in an inheritance is called single level.

·        Sub-class extends Super-class

·        Sub-interface extends Super-interface

·        Sub-class implements Super-interface

Example –

class Add{

          int num1,num2,result=0;

          public void add()

          {

                   result=num1+num2;

          }

}

class Sub extends Add{

          public void sub()

          {

                   result=num1-num2;

          }

}

public class Test2 {

          public static void main(String[] args) {

                   Sub s = new Sub();

                   s.num1=50;

                   s.num2=30;

                   s.add();

                   System.out.println(s.result);

                   s.sub();

                   System.out.println(s.result);

                   s.sub();

          }

}

Output –

80

20

Note – In the above example Sub class extends all the properties of Add class. So we have created an object of Subclass, but still we can directly acces the properties of its Super class.

2. Multi level inheritance – If more than two classes are participating in inheritance relation vertically, we call it as multilevel inheritance.

Example –

class Add{

          int num1,num2,result=0;

          public void add()

          {

                   result=num1+num2;

          }

}

class AddSub extends Add{

          public void sub()

          {

                   result=num1-num2;

          }

}

class AddSubMul extends AddSub

{

          public void mult()

          {

                   result=num1*num2;

          }       

}

public class Test2 {

          public static void main(String[] args) {

                   AddSubMul s = new AddSubMul();

                   s.num1=50;

                   s.num2=30;

                   s.add();

                   System.out.println(s.result);

                   s.sub();

                   System.out.println(s.result);

                   s.mult();

                   System.out.println(s.result);

          }

}

Output –

80

20

1500

Note – In the above example AddSub extends Add and AddSubMul extends AddSub, so all the properties of above parent class is being inherited by the sub class AddSubMul.

3. Hierarchical inheritance – If we derive multiple sub classes from a single super class, we call it as Hierarchical inheritance

Example –

class Add{

          int num1,num2,result=0;

          public void add()

          {

                   result=num1+num2;

          }

}

class AddSub extends Add{

          public void sub()

          {

                   result=num1-num2;

          }

}

class AddMul extends Add

{

          public void mult()

          {

                   result=num1*num2;

          }       

}

public class Test2 {

          public static void main(String[] args) {

                   AddSub a = new AddSub();

                   a.num1=15;

                   a.num2=10;

                   a.add();

                   System.out.println(a.result);

                   a.sub();

                   System.out.println(a.result);

                   AddMul a1 = new AddMul();

                   a1.num1=5;

                   a1.num2=3;

                   a1.add();

                   System.out.println(a1.result);

                   a1.mult();

                   System.out.println(a1.result);

          }

}

Output –

25

5

8

15

4. Hybrid inheritance – Developing an inheritance by combining other types of inheritances is called hybrid inheritance.

For more details refer tutorials on types of classes.

5. Multiple inheritance – Deriving a sub class from multiple super class is called multiple inheritances. Java does not support multiple inheritance with classes, but it supports with interfaces.

For more details refer tutorials on types of classes.