Java Program to calculate area and circumference of circle

In this tutorial we will see how to calculate area and circumference of circle in Java. There are two ways to do this:

1) With user interaction: Program will prompt user to enter the radius of the circle
2) Without user interaction: The radius value would be specified in the program itself.

Program 1:

/**
 * @author: BeginnersBook.com
 * @description: Program to calculate area and circumference of circle
 * with user interaction. User will be prompt 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:

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

Program 2:

/**
 * @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 CircleDemo2
{
   public static void main(String args[])
   {
      int radius = 3;
      double area = Math.PI * (radius * radius);
      System.out.println("The area of circle is: " + area);
      double circumference= Math.PI * 2*radius;
      System.out.println( "The circumference of the circle is:"+circumference) ;
   }
}

Output:

The area of circle is: 28.274333882308138
The circumference of the circle is:18.84955592153876