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Inheritance in Java

Last updated on 22nd Sep 2020, Artciles, Blog, Software Engineering

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The process by which one class acquires the properties(data members) and functionalities(methods) of another class is called inheritance. The aim of inheritance is to provide the reusability of code so that a class has to write only the unique features and rest of the common properties and functionalities can be extended from the other class.

Child Class:

The class that extends the features of another class is known as child class, subclass or derived class.

Parent Class:

The class whose properties and functionalities are used(inherited) by another class is known as parent class, super class or Base class.

Syntax: Inheritance in Java

To inherit a class we use an extended keyword. Here class XYZ is child class and class ABC is parent class. The class XYZ is inheriting the properties and methods of ABC class.

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  • class XYZ extends ABC

    {

    }

Example

In this example, we have a base class Teacher and a sub class PhysicsTeacher. Since class PhysicsTeacher extends the designation and college properties and work() method from base class, we need not to declare these properties and methods in subclass.

Here we have collegeName, designation and work() method which are common to all the teachers so we have declared them in the base class, this way the child classes like MathTeacher, MusicTeacher and PhysicsTeacher do not need to write this code and can be used directly from base class.

  • class Teacher {

       String designation = “Teacher”;

       String collegeName = “ABC”;

       void does(){

    System.out.println(“Teaching”);

       }

    }

     

    public class PhysicsTeacher extends Teacher{

       String mainSubject = “Physics”;

       public static void main(String args[]){

    PhysicsTeacher obj = new PhysicsTeacher();

    System.out.println(obj.collegeName);

    System.out.println(obj.designation);

    System.out.println(obj.mainSubject);

    obj.does();

       }

    }

Output:

ABC

Teacher

Physics

Teaching

Based on the above example we can say that PhysicsTeacher IS-A Teacher. This means that a child class has an IS-A relationship with the parent class. This is inheritance is known as IS-A relationship between child and parent class

Types of Inheritance

Single Inheritance in Java

Single Inheritance is the simple inheritance of all, When a class extends another class(Only one class) then we  call it Single inheritance. The below diagram represents the single inheritance in java where Class B extends only one class Class A. 

Here Class B will be the Sub class and Class A will be one and only Super Class.

Single-Inheritance-in-Java

Single Inheritance Example

  • public class ClassA 

    {

        public void dispA()

        {

            System.out.println(“disp() method of ClassA”);

        }

    }

    public class ClassB extends ClassA 

    {

        public void dispB()

        {

            System.out.println(“disp() method of ClassB”);

        }

        public static void main(String args[])

        {

            //Assigning ClassB object to ClassB reference

            ClassB b = new ClassB();

            //call dispA() method of ClassA

            b.dispA();

            //call dispB() method of ClassB

            b.dispB();

        }

    }

Output :

disp() method of ClassA

disp() method of ClassB

Multiple Inheritance in Java

Multiple Inheritance is nothing but one class extending more than one class. Multiple Inheritance is basically not supported by many Object Oriented Programming languages such as Java, Small Talk, C# etc.. (C++ Supports Multiple Inheritance). As the Child class has to manage the dependency of more than one Parent class. But you can achieve multiple inheritance in Java using Interfaces.

Multiple-Inheritance-in-Java
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Multilevel Inheritance in Java

In Multilevel Inheritance a derived class will be inheriting a parent class and as well as the derived class act as the parent class to other class. As seen in the below diagram. ClassB inherits the property of ClassA and again ClassB act as a parent for ClassC. In Short ClassA parent for ClassB and ClassB parent for ClassC.

Multilevel-Inheritance-in-Java

MultiLevel Inheritance Example

  • public class ClassA 

    {

        public void dispA()

        {

            System.out.println(“disp() method of ClassA”);

        }

    }

    public class ClassB extends ClassA 

    {

        public void dispB()

        {

            System.out.println(“disp() method of ClassB”);

        }

    }

    public class ClassC extends ClassB

    {

        public void dispC()

        {

            System.out.println(“disp() method of ClassC”);

        }

        public static void main(String args[])

        {

            //Assigning ClassC object to ClassC reference

            ClassC c = new ClassC();

            //call dispA() method of ClassA

            c.dispA();

            //call dispB() method of ClassB

            c.dispB();

            //call dispC() method of ClassC

            c.dispC();

        }

    }

Output :

disp() method of ClassA

disp() method of ClassB

disp() method of ClassC

Hierarchical Inheritance in Java

In Hierarchical inheritance one parent class will be inherited by many sub classes. As per the below example ClassA will be inherited by ClassB, ClassC and ClassD. ClassA will be acting as a parent class for ClassB, ClassC and ClassD.

Hierarchical-Inheritance-in-Java

Hierarchical Inheritance Example

  • public class ClassA 

    {

        public void dispA()

        {

            System.out.println(“disp() method of ClassA”);

        }

    }

    public class ClassB extends ClassA 

    {

        public void dispB()

        {

            System.out.println(“disp() method of ClassB”);

        }

    }

    public class ClassC extends ClassA

    {

        public void dispC()

        {

            System.out.println(“disp() method of ClassC”);

        }

    }

    public class ClassD extends ClassA

    {

        public void dispD()

        {

            System.out.println(“disp() method of ClassD”);

        }

    }

    public class HierarchicalInheritanceTest 

    {

        public static void main(String args[])

        {

            //Assigning ClassB object to ClassB reference

            ClassB b = new ClassB();

            //call dispB() method of ClassB

            b.dispB();

            //call dispA() method of ClassA

            b.dispA();

            

            

            //Assigning ClassC object to ClassC reference

            ClassC c = new ClassC();

            //call dispC() method of ClassC

            c.dispC();

            //call dispA() method of ClassA

            c.dispA();

            

            //Assigning ClassD object to ClassD reference

            ClassD d = new ClassD();

            //call dispD() method of ClassD

            d.dispD();

            //call dispA() method of ClassA

            d.dispA();

        }

    }

Output :

disp() method of ClassB

disp() method of ClassA

disp() method of ClassC

disp() method of ClassA

disp() method of ClassD

disp() method of ClassA

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Hybrid Inheritance in Java

Hybrid Inheritance is the combination of both Single and Multiple Inheritance. Again Hybrid inheritance is also not directly supported in Java only through the interface we can achieve this. Flow diagram of the Hybrid inheritance will look like below. As you can ClassA will be acting as the Parent class for ClassB & ClassC and ClassB & ClassC will be acting as Parent for ClassD.

Hybrid-Inheritance-in-Java

This is a guide to Inheritance in Java. Here we discuss the importance and different types of inheritance in java along with syntax, examples and code implementation. 

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