How to calculate Area and Circumference of Circle through a simple Java program ?

package com.hubpages.example;

import java.util.Scanner;

public class CircleDemo {

	public static void main(String[] args) {

		// Step 1 --- We will create a Scanner object,
		// it will take System.in object in its constructor
		// This provide Scanner capability of reading
		// user input to console

		Scanner scanner = new Scanner(System.in);

		// Step 2 --- We will ask the user to enter the 
		// value of radius of the circle for which he wants 
		// to calculate the area and circumference of circle

		System.out.println("Enter the Radius of Circle --- ");

		// Step 3 --- User enters radius of circle on the console
		// and it is been read by scanner object by the method 
		// nextDouble() and return value is been stored in the radius
		// variable

		double radius = scanner.nextDouble();

		// Step 4 --- Two variable created for storing the area and 
		// circumference of circle

		double area = 0;
		double circumference = 0;

		System.out.println("Calculating Area and Circumference of Circle ---- ");

		// Step 5 --- Formula for Area of Circle is pi * r * r
		// We have used Math class final variable called as PI
		// which stores the value of pi of Circle
		// Area is calculated and stored in the area variable

		area = Math.PI * radius * radius;

		// Step 6 --- Formula for Circumference of Circle is 2 * pi * r
		// We have used Math class final variable called as PI
		// which stores the value of pi of Circle
		// Circumference is calculated and stored in the circumference variable

		circumference = 2 * Math.PI * radius;

		// Step 7 --- Output is displayed on the console

		System.out.println("The Area of Circle is --- " + area);
		System.out.println("The Circumference of Circle is --- " + circumference);
	}

}