Question

java

Create a program that defines a class called circle. Circle should have a member

variable called radius that is used to store the radius of the circle. Circle should also

have a member method called calcArea that calculates the area of the circle using

the formula area = pi*r^2. Area should NOT be stored in a member variable of

circle to avoid stale data.

Use the value 3.14 for PI.

For now, make radius public and access it directly using the dot operator. Do not

worry about input validation for now. In main instantiate two objects of class circle

and have the user enter a radius for each. Store the radii in the appropriate objects'

member variables, then print the radius and area of each circle using the member

variable and function.

public class circle

{

public double radius = 0;

void printArea()

{

System.out.println(radius * radius * 3.14159);

}

}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

Modify what is above so that the radius variable in class circle is private. Write a setter

and getter method for radius, as well as a default constructor that initializes radius

to 0 and a constructor that takes one parameter for radius. If radius is given as a

negative in a call to the setter or the constructor set it to 0 instead.

In main, instantiate (declare/create) and use circle objects as needed to prove that

all of your functions, including both constructors, work properly (construct a test

case for your class in main).

Answer 1

Dear Student ,

As per requirement submitted above kindly find below solution.

Demonstration 1:

circle.java :

//Java class
public class circle {
   //member variable
   public double radius = 0;
   //method to calculate area
   public void calcArea()
   {
       //print area of circle
       System.out.println("Area of circle with radius "+this.radius+" is "+(this.radius * this.radius * 3.14159));
   }
}
****************************

CircleTest.java :

//import package
import java.util.*;
//Java class
public class CircleTest {
   //entry point of the program , main() method
   public static void main(String[] args) {
       //creating object of Scanner class
       Scanner sc=new Scanner(System.in);
       //asking user radius
       System.out.print("Enter Radius 1: ");
       double radius1=sc.nextDouble();//reading radius
       //asking user radius
       System.out.print("Enter Radius 2: ");
       double radius2=sc.nextDouble();//reading radius
       //creating object of Circle class
       circle c1=new circle();
       c1.radius=radius1;//set radius
       //call method to print area
       c1.calcArea();
       //creating object of Circle class
       circle c2=new circle();
       c2.radius=radius2;//set radius
       //call method to print area
       c2.calcArea();
      
   }

}

==================================

Output :Compile and Run CircleTest.java to get the screen as shown below

Screen 1:

******************************

Demonstration 2:

circle.java :

//Java class
public class circle {
   //member variable
   private double radius;
   //default constructor
   public circle()
   {
       this.radius=0;//set radius to 0
   }
   //constructor with one parameter
   public circle(double r)
   {
       setRadius(r);//calling setter method
   }
   //getter method
   public void setRadius(double r)
   {
       //checking value of radius
       if(r<0)
       {
           //if radius is negative then
           this.radius=0;//set radius to 0
       }
       else {
           this.radius=r;
       }
   }
   //getter method
   public double getRadius()
   {
       return this.radius;//return radius
   }
   //method to calculate area
   public void calcArea()
   {
       //print area of circle
       System.out.println("Area of circle with radius "+getRadius()+" is "+(getRadius() * getRadius() * 3.14159));
   }
}
*****************************

CircleTest.java :

//import package
import java.util.*;
//Java class
public class CircleTest {
   //entry point of the program , main() method
   public static void main(String[] args) {
       //creating object of Scanner class
       Scanner sc=new Scanner(System.in);
       //creating object of Circle class
       circle c1=new circle();
       //asking user radius
       System.out.print("Enter Radius 1: ");
       c1.setRadius(sc.nextDouble());//reading radius
       //asking user radius
       System.out.print("Enter Radius 2: ");
       double radius=sc.nextDouble();//reading radius
       //creating object of Circle class
       circle c2=new circle(radius);      
       //call method to print area
       c1.calcArea();      
       //call method to print area
       c2.calcArea();
      
   }

}
==================================

Screen 1:

Screen 2:When radius is negative

NOTE :PLEASE FEEL FREE TO PROVIDE FEEDBACK ABOUT THE SOLUTION.