Java Program to Calculate Area and Circumference of Circle

In this tutorial, you will learn how to calculate area and circumference of circle in Java. We will see two programs, in the first program, the radius value is initialized in the program and in the second program, the radius value is entered by the user.

Formula for area and circumference of circle

Area of circle = πr2
Circumference of circle = 2πr

Here π value is 22/7 or 3.14 (rounding of the output of 22/7 upto 2 decimal places).

1. Program to calculate area and circumference of Circle

In this program, radius value is specified in the program and we are calculating the area and circumference using the above mentioned formulas.

You may be wondering why we are using printf() method instead of print() or println(), this is to round of the output upto two decimal points, the format specifier %.2f rounds of the decimal points to two decimal points. If we use the print() method then the program displays the value upto several decimal points, however there is nothing wrong using that as well.

/**
 * @author: BeginnersBook.com
 * @description: Program to calculate area and circumference of
 * circle without user interaction. You need to specify the
 * radius value in program itself.
 */
class JavaExample
{
  public static void main(String args[])
  {
    int radius = 3;
    //formula to calculate area of circle
    double area = Math.PI * (radius * radius);
    System.out.printf("Area is: %.2f", area);

    //formula to calculate circumference of circle
    double circumference= Math.PI * 2*radius;
    System.out.printf( "\nCircumference is: %.2f",circumference) ;
  }
}

Output:

2. Radius value is entered by user

In this program, the radius value is entered by the user. We are using Scanner class to capture the user input and store it into a variable. The logic is same as the above program.

/**
 * @author: BeginnersBook.com
 * @description: Program to calculate area and circumference of circle
 * with user interaction. User will be prompted to enter the radius and 
 * the result will be calculated based on the provided radius value.
 */
import java.util.Scanner;
class CircleDemo
{
   static Scanner sc = new Scanner(System.in);
   public static void main(String args[])
   {
      System.out.print("Enter the radius: ");
      /*We are storing the entered radius in double
       * because a user can enter radius in decimals
       */
      double radius = sc.nextDouble();
      //Area = PI*radius*radius
      double area = Math.PI * (radius * radius);
      System.out.println("The area of circle is: " + area);
      //Circumference = 2*PI*radius
      double circumference= Math.PI * 2*radius;
      System.out.println( "The circumference of the circle is:"+circumference) ;
   }
}

Output: As you can see there is a number of digits after decimal point, you can round of this and limit the digits after decimal point using the format specifier in printf() method as shown in the example 1 above.

Enter the radius: 1
The area of circle is: 3.141592653589793
The circumference of the circle is:6.283185307179586

Related Java Programs

• Java Program to find area of Geometric figures
• Java Program to calculate area of Rectangle
• How to print Pattern in Java
• Java Program to Calculate Simple Interest