Program to demonstrate Single Inheritance

Inheritance is the property in which objects of one class acquires the properties of other class. This is the one of feature of Java known as Reusability. With the use of inheritance, the information is made manageable in a hierarchical order. A class that is inherited is called a superclass. The class that does the inheriting is called subclass. It inherits all of the instance variables and methods defined by the superclass and adds its own, unique elements. There are following types of Inheritance:
  1. Single Inheritance (only one superclass and subclass)
  2. Multiple Inheritance (several super classes for a subclass)
  3. Hierarchical Inheritance (one super class with many subclasses)
  4. Multilevel Inheritance (subclass is super class of another class)
  5. Hybrid Inheritance (combination of above four types)
Java supports the first three types of inheritance. Java does not support Multiple inheritance and hybrid inheritance. Java does not directly implement the multiple inheritance. You can achieve this by making use of the new concept in Java called Interface. The syntax of single inheritance is given below:
class <superclass-name> {
    // Body of superclass

class <subclass-name> extends <superclass-name> {
 // Body of subclass

This a program for the single inheritance, in that AA is a superclass which has one variable i and one method showI( ). Next the class AA is get inherited in class BB which also have one variable j and one method showJ( ). Now class BB have variable i, method showI( ) which is inherited from parent of BB that is from class AA and its own data member and method. Now in SingleInhDemo class we have created an object AA and BB classes, initialized the data members and called the methods of classes.

Note that after compiling the file the three .class files will be created namely "AA.class", "BB.class" and "SingleInhDemo.class".

class AA {
 int i;
 void showI() {
  System.out.println("i = "+i);

class BB extends AA {

 int j;
 void showJ() {
  System.out.println("j = "+j);

public class SingleInhDemo {

 public static void main(String[] args) {
  BB b = new BB();    // Creating object of subclass
  b.i = 56;      // Assign value to i of AA class
  b.j = 23;      // Assign value to j of BB class
  b.showI();     // Call method showI( ) of AA class
  b.showJ();     // Call method showJ( ) of BB class
C:\>java SingleInhDemo
i = 56
j = 23

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