Implementation of Different Type of Inheritance

Implementation of Different Types of Inheritance

Single Inheritance

• The class which is inherited is called the base class or the superclass and the class that does the inheriting is called the derived class or the subclass.

• The method defined in base class can be used in derived class. There is no need to redefine the method in derived class. Thus inheritance promotes software reuse.

• The subclass can be defined as follows -

class nameofSubclass extends superclass

{

variable declarations

method declarations

}

Note that the keyword extends represents that the properties of superclass are extended to the subclass. Thus the subclass will now have both the properties of its own class and the properties that are inherited from superclass.

• Following is a simple Java program that illustrates the concept of single inheritance -

Java Program[InheritDemo1.java]

class A

{

int a;

void set_a(int i)

{

a=i;

}

void show_a()

{

System.out.println("The value of a= "+a);

}

}

class B extends A //extending the base class A

{

int b;

void set_b(int i)

{

b=i;

}

void show_b()

{

System.out.println("The value of b= "+b);

}

void mul()

{

int c;

c=a*b;

System.out.println(" The value of c= "+c);

}

}

class InheritDemo1

{

public static void main(String args[])

{

A obj_A=new A();

B obj_B=new B();

Note that object of class B is accessing method of class A

obj_B.set_a(10);

obj_B.set_b(20);

obj_B.show_a();

obj_B.show_b();

obj_B.mul();

}

}

Output

F:\test>javac InheritDemo1.java

F:\test>java Inherit Demo1

The value of a= 10

The value of b= 20

The value of c= 200

Program Explanation

In above program, we have created two classes: class A and B. In class A we have declared one integer a and in class B we have declared an integer b. There are two methods defined in class A namely: set_a and show_a. Similarly, in class B there are two methods defined namely: set_b and show_b. As the name suggests these methods are for setting the values and for showing the contents.

In the class InheriDemo1, in the main function we have created two objects for class A and class B. The program allows us to access the variable a (belonging to class A) and the variable b (belonging to class B) using the object for class B. Thus it is said that class B has inherited value of variable a.

The class A is called Superclass and the class B is called Subclass. A Superclass is also called as parent class or base class. Similarly, the Subclass is also called as child class or derived class.

Ex. 2.8.1 : Write a java program to calculate area of rectangle using the single inheritance.

Sol. :

class Shape

{

int len,br;

void setValues(int a,int b)

{

len=a;

br=b;

}

}

class Rectangle extends Shape

{

int area()

{

return len*br;

}

}

class test

{

public static void main(String args[])

{

Rectangle r=new Rectangle();

r.setValues(10,20);

System.out.println("\n Area of rectangle is "+r.area());

}

}

Output

Multilevel Inheritance

The multilevel inheritance is a kind of inheritance in which the derived class itself derives the subclasses further.

In the following program, we have created a base class A from which the subclass B is derived. There is a class C which is derived from class B. In the function main we can access any of the

field in the class hierarchy by creating the object of class C.

Java Program[MultiLvilnherit.java]

class A

{

int a;

void set_a(int i)

{

a=i;

}

void show_a()

{

System.out.println("The value of a= "+a);

}

}

class B extends A

{

int b;

void set_b(int i)

{

b=i;

}

void show_b()

{

System.out.println("The value of b= "+b);

}

class C extends B

{

int c;

void set_c(int i)

{

c=i;

}

void show_c()

{

System.out.println("The value of c= "+c);

}

void mul()

{

int ans;

ans=a*b*c;

System.out.println(" The value of ans = "+ans);

}

}

class MultiLvlInherit

{

public static void main(String args[])

{

A obj_A=new A();

B obj_B=new B();

C obj_C=new C();

obj_C.set_a(10);

obj_C.set_b(20);

obj_C.set_c(30);

obj_C.show_a();

obj_C.show_b();

obj_C.show_c();

obj_C.mul();

}

}

Output

The value of a= 10

The value of b= 20

The value of c= 30

The value of ans= 6000

Ex. 2.8.2 Declare a class called employee having employee_id and employee_name as members. Extend class employee to have a subclass called salary having designation and monthly_salary as members. Define following:

Required constructors.

A method to find and display all details of employees drawing salary more than 20000/-.

Method main for creating an array for storing these details given as command line argumentsand showing usage of above methods.

Sol. :

class employee

{

int employee_id;

String employee_name;

}

class salary extends employee //derived class

{

String designation;

double monthly_salary;

salary() //default constructor

{}

salary(int employee_id,String employee_name,String designation, double monthly_salary) //parameterised consruct.

{

this.employee_id = employee_id;

this.employee_name = employee_name;

this.designation = designation;

this.monthly_salary = monthly_salary;

}

void fun(String emp[][]) //Function displaying salary>20000

{

for(int i=0;i<emp.length;i++)

{

if( (Double.parseDouble(emp[i][3])) > 20000)

{

System.out.println("\nEmployee Drawing Salary More than 20000/- :");

System.out.println("Id = "+emp[i][0]);

System.out.println("Name = "+emp[i][1]);

System.out.println("Designation = "+emp[i][2]);

System.out.println("Salary = "+emp[i][3]);

System.out.println("--------------------------------");

}

}

}

}

public class employeetest

{

public static void main(String args[])

{

salary obj[] = new salary[5];

String Details[][];

obj[0] = new salary(1,"AAA","Accountant", 12000);

obj[1] = new salary(2, "BBB","Manager", 30000);

obj[2] = new salary(3,"CCC","Executive", 2000);

obj[3] = new salary(4, "DDD","CEO",50000);

obj [4] = new salary();                                                     

try

{

obj[4].employee_id = Integer.parseInt(args[0]);

obj [4].employee_name = args[1];

obj [4].designation = args[2];

obj [4].monthly_salary = Double.parseDouble(args[3]);

}

catch(NumberFormatException e)

{

System.out.println("Exception: "+e);

}

Details = new String[obj.length][4];

for(int i=0;i<obj.length;i++)

{

Details[i][0] = String.valueOf(obj[i].employee_id);

Details[i][1] = obj[i].employee_name;

Details[i][2] = obj[i].designation;

Details[i][3] = String.valueOf(obj[i].monthly_salary);

}

obj [4].fun(Details);

}

}

Output

E:\test>javac employeetest.java

E:\test>java employeetest 5 EEE Manager 20000

Employee Drawing Salary More than 20000/- :

Id = 2

Name = BBB

Designation = Manager

Salary = 30000.0

­-------------------------------------------

Employee Drawing Salary More than Rs. 20000/- :

Id = 4

Name DDD

Designation = CEO

Salary = 50000.0

-------------------------------------------

Ex. 2.8.3 Create a Java class Shape with constructor to initialize the one parameter "dimension". Now create three subclasses of Shape with following methods:

(i) n"Circle" with methods to calculate the area and circumference of the circle with dimension as radius.

(ii) "Square" with methods to calculate the area and length of diagonal of square with dimension as length of one side.

(iii) "Sphere" with methods to calculate the volume and surface area of sphere with dimension as radius of the sphere. Write appropriate main method to create object of each class and test every method

Sol.:

class Shape

{

double dimension;

Shape()

{

dimension=0;

}

}

class Circle extends Shape

{

Circle(double r)

{

dimension = r;

}

void display()

{

System.out.println("------------------------------");

System.out.println("The radius of circle is: "+dimension);

}

double area()

{

System.out.print("Area Of Circle: ");

return (3.14* dimension* dimension);

}

double circum()

{

System.out.print("Circumference Of Circle: ");

return (2*3.14* dimension);

}

}

class Square extends Shape

{

Square (double d)

{

dimension = d;

}

void display()

{

System.out.println("---------------------------------");

System.out.println("The side of square is: "+dimension);

}

double area()

{

System.out.print("Area Of Square: ");

return (dimension* dimension);

}

double LenDiagonal()

{

System.out.print("Length of Diagonal of Square: ");

return (dimension* Math.sqrt(2));

}

}

class Sphere extends Shape

{

Sphere(double r)

{

dimension = r;

}

void display()

{

System.out.println("------------------------------------");

System.out.println("The radius of sphere is: "+dimension);

}

double area()

{

System.out.print("Surface Area Of Sphere: ");

return (4*3.14*dimension* dimension);

}

double volume()

{

System.out.print("Volume of Sphere: ");

return ((4/3)*3.14* dimension* dimension* dimension);

}

}

class InheritanceDemo

{

public static void main(String args[])

{

Circle cir = new Circle(10);

cir.display();

System.out.println(cir.area());

System.out.println(cir.circum());

Square sq = new Square(10);

sq.display();

System.out.println(sq.area());

System.out.println(sq.LenDiagonal());

Sphere sph = new Sphere(10);

sph.display();

System.out.println(sph.area());

System.out.println(sph.volume());

 

}

}

Output

---------------------------------------------

The radius of circle is: 10.0

Area Of Circle: 314.0

Circumference Of Circle: 62.800000000000004

--------------------------------------------

The side of square is: 10.0

Area Of Square: 100.0

Length of Diagonal of Square: 14.142135623730951

--------------------------------------------

The radius of sphere is: 10.0

Surface Area Of Sphere: 1256.0

Volume of Sphere: 3140.0

Review Questions

1. What is inheritance? Write a program for inheriting a class.

2.What is inheritance? With diagrammatic illustrations and Java programs illustrate different types of inheritance. Give self explanatory comments in your program.

3. Define Inheritance. With diagrammatic illustration and java programs illustrate the different types of inheritance with an example.