Question

/**
 * Chapter 6
 * Programming Challenge 1: Area Class
 * This program demonstrates the Area class.
 */

public class AreaDemo
{
   public static void main(String[] args)
   {
      // Get the area of a circle with a radius of 20.0.
      System.out.println("The area of a circle with a " +
                         "radius of 20.0 is " + 
                         Area.getArea(20.0));

      // Get the area of a rectangle with a length of 10
      // and a width of 20.
      System.out.println("The area of a rectangle with a " +
                         "length of 10 and a width of 20 is " + 
                         Area.getArea(10, 20));

      // Get the area of a cylinder with a radius of 10.0
      // and a height of 15.0.
      System.out.println("The area of a cylinder with a " +
                         "radius of 10.0 and a height" +
                         "of 15.0 is " + 
                         Area.getArea(10.0, 15.0));
   }
}

Answer 1

SOURCE CODE:

*Please follow the comments to better understand the code.

**Please look at the Screenshot below and use this code to copy-paste.

***The code in the below screenshot is neatly indented for better understanding.

Area class

/* 
This class demonstrates the concept of OVERLOADING methods.
 */
 
public class Area
{
    // only one parameter, CIRCLE
    public static double getArea(double radius)
    {
        return Math.PI * radius * radius;
    }

    // TWO parameters (int,int), it's a RECTANGLE
    public static double getArea(int length, int width)
    {
        return length*width;
    }

    // TWO parameters (double,double), it's a CYLINDER
    public static double getArea(double radius, double height)
    {
        return (2*Math.PI*radius) * (radius + height);
    }
}

====================

AREA DEMO

/**
 * Chapter 6
 * Programming Challenge 1: Area Class
 * This program demonstrates the Area class.
 */

public class AreaDemo
{
    public static void main(String[] args)
    {
        // Get the area of a circle with a radius of 20.0.
        System.out.println("The area of a circle with a " +
                "radius of 20.0 is " +
                Area.getArea(20.0));

        // Get the area of a rectangle with a length of 10
        // and a width of 20.
        System.out.println("The area of a rectangle with a " +
                "length of 10 and a width of 20 is " +
                Area.getArea(10, 20));

        // Get the area of a cylinder with a radius of 10.0
        // and a height of 15.0.
        System.out.println("The area of a cylinder with a " +
                "radius of 10.0 and a height" +
                "of 15.0 is " +
                Area.getArea(10.0, 15.0));
    }
}

===============

OUTPUT: