Java program to calculate area and circumference of circle

In this section, we will create a Java program to calculate the area and circumference of the circle.

Area of Circle Formulas

When the radius is known:

Java Program to Calculate Area and Circumference of Circle

When the diameter is known:

When the circumference is known:

Where,

A: is an area of a circle

π: is a constant, whose value is 3.1415 or 22/7.

r: is the radius of a circle

d: is the diameter of a circle

C: is the circumference of a circle

Let's implement the above formulas in a Java program and find the area of the circle.

In the following Java program, we have used a Java switch case because we have used three scenarios to find the area of the circle. The user provides an option and the switch statement executes the corresponding case. The three scenarios are: if the radius is known, if the diameter is known, if the circumference is known.

Note: Throughout this section, we have used a constant Pi (π). To access the value of the constant, we have used a static field PI of the Math class. It is defined in Math class as follows:

The double value that is closer than any other to pi, the ratio of the circumference of a circle to its diameter. Its value is 3.141592653589793. Instead of using Math.PI we can also write the value of pi (3.14 or 22/7) directly.

AreaOfCircle.java

import java.util.Scanner;
import java.lang.Math;
public class AreaOfCircle
{
public static void main(String[] args) 
{
int option;
double radius, circumference, diameter, area;  
//object of the Scanner class
Scanner sc=new Scanner (System.in);
//options available
System.out.println("1. If the radius is known"); 
System.out.println("2. If the diameter is known");  
System.out.println("3. If the circumference is known");  
System.out.print("Enter your choice: ");  
//taking an option as input from the user
option=sc.nextInt();
switch(option)
{  
//Case statements  
case 1: 
    System.out.print("Enter the radius of the circle: "); 
    radius=sc.nextDouble();
    area=(Math.PI*(radius*radius));
    System.out.print("The area of the circle is: "+area); 
    break;  
case 2:
    System.out.print("Enter the diameter of the circle: "); 
    diameter=sc.nextDouble();
    area=Math.PI*(diameter*diameter)/4;
    System.out.print("The area of the circle is: "+area); 
    break; 
case 3: 
    System.out.print("Enter the circumference of the circle: "); 
    circumference=sc.nextDouble();
    area=(circumference*circumference)/(4*Math.PI);
    System.out.print("The area of the circle is: "+area); 
    break;  
//default case statement executes when an invalid choice is entered
default:System.out.println("invalid choice!");   
}  
}  
}  

Output 1:

1. If the radius is known
2. If the diameter is known
3. If the circumference is known
Enter your choice: 1
Enter the radius of the circle: 6
The area of the circle is: 113.09733552923255

Output 2:

1. If the radius is known
2. If the diameter is known
3. If the circumference is known
Enter your choice: 2
Enter the diameter of the circle: 16
The area of the circle is: 201.06192982974676

Output 3:

1. If the radius is known
2. If the diameter is known
3. If the circumference is known
Enter your choice: 3
Enter the circumference of the circle: 30
The area of the circle is: 71.6197243913529

Output 4:

1. If the radius is known
2. If the diameter is known
3. If the circumference is known
Enter your choice: 4
invalid choice!

In the following Java program, we have calculated the circumference of the circle. The formula that we have used in the program is:

Circumference (C) =2πr

CircumferenceOfCircle.java

import java.util.Scanner;
import java.lang.Math;
public class CircumferenceOfCircle
{
public static void main(String[] args) 
{
double circumference, radius;
//object of the Scanner class
Scanner sc=new Scanner (System.in);
System.out.print("Enter the radius of the circle: ");
//reading radius from the user
radius=sc.nextDouble();
//formula to calculate circumference of the circle
circumference= Math.PI*2*radius;
//prints the circumference
System.out.println("The circumference of the circle is: "+circumference);
}  
}  

Output:

Enter the radius of the circle: 20
The circumference of the circle is: 125.66370614359172

In the following program, we have calculated the area and circumference of the circle in a single program.

AreaAndCircumferenceOfCircle.java

import java.util.Scanner;
public class AreaAndCircumferenceOfCircle
{
public static void main(String args[])
{
double circumference, area; 
int radius;
//object of the Scanner class
Scanner sc=new Scanner (System.in);
System.out.print("Enter the radius of the circle: ");
radius=sc.nextInt();
//calculating area of circle
area=Math.PI*(radius*radius);
//prints the calculated area
System.out.println("The area of the circle is: "+area);
//calculating circumference of circle
circumference=Math.PI*2*radius;
//prints the calculated circumference
System.out.println("The circumference of the circle is: "+circumference);
}
}

Output:

Enter the radius of the circle: 6
The area of the circle is: 113.09733552923255
The circumference of the circle is: 37.69911184307752

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Java program to calculate area and circumference of circle

Area of Circle Formulas

Note: Throughout this section, we have used a constant Pi (π). To access the value of the constant, we have used a static field PI of the Math class. It is defined in Math class as follows:

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