4.Program to Accept value of Radius and Calculate Area of Circle.

 

class CalculateCircleAreaExample
{
    public static void main(String[] args)
    {
        int radius = 3;
        System.out.println("The radius of the circle is " + radius);
 /*
         * Area of a circle is pi * r * r where r is a radius of a circle.
  */
        // NOTE : use Math.PI constant to get value of pi
        double area = Math.PI * radius * radius;
        System.out.println("Area of a circle is " + area);
    }
}