difficulty with x , y coordinate
<p>I am trying to solve one problem from Liang's book I have done most of it but I do not understand the part with the x and y coordinates.I have two classes TestRegularPolygon which is the driver class for RegularPolygon. The formula for the area is not currently correct I will deal with it later. I  am using eclipse the code is compiling and running if anyone can give me some idea how to do it I would appreciate it!</p>

<p>(Geometry: n-sided regular polygon) In an n-sided regular polygon all sides
have the same length and all angles have the same degree (i.e., the polygon is
both equilateral and equiangular). Design a class named RegularPolygon that
contains:</p>

<ul>
<li>A private int data field named n that defines the number of sides in the polygon
with default value 3.</li>
<li>A private double data field named side that stores the length of the side with
default value 1.</li>
<li>A private double data field named x that defines the x-coordinate of the center
of the polygon with default value 0.</li>
<li>A private double data field named y that defines the y-coordinate of the center
of the polygon with default value 0.</li>
<li>A no-arg constructor that creates a regular polygon with default values.</li>
<li>A constructor that creates a regular polygon with the specified number of sides
and length of side, centered at (0, 0).</li>
<li>A constructor that creates a regular polygon with the specified number of sides,
length of side, and x-and y-coordinates.</li>
<li>The accessor and mutator methods for all data fields.</li>
<li>The method getPerimeter() that returns the perimeter of the polygon.</li>
<li>The method getArea() that returns the area of the polygon. The formula for
computing the area of a regular polygon is</li>
</ul>

<p>Draw the UML diagram for the class. Implement the class. Write a test program
that creates three RegularPolygon objects, created using the no-arg constructor,
using RegularPolygon(6, 4), and using RegularPolygon(10, 4, 5.6,
7.8). For each object, display its perimeter and area.</p>

<pre><code>public class RegularPolygon 
{
    private int n; //number of sides of the polygon
    private double side; //store the length of the side
    private double x; // x coordinate
    private double y; //y coordinate

    RegularPolygon()
    {
        n = 3;
        side = 1;
        x = 0; 
        y = 0;
    }

    RegularPolygon(int n, double side)
    {
        this.n = n;
        this.side = side;
        x = 0;
        y = 0;
    }

    RegularPolygon(int n, double side, double x, double y)
    {
        this.n = n;
        this.side = side;
        this.x = x;
        this.y = y;
    }

    public void setN(int then)
    {
        n = then;
    }

    public int getN()
    {
        return n;
    }

    public void setSide(double theside)
    {
        side = theside;
    }

    public double getSide()
    {
        return side;
    }

    public void setX(int thex)
    {
        x = thex;
    }

    public double getX()
    {
        return x;
    }

    public void setY(int they)
    {
        y = they;
    }

    public double getY()
    {
        return y;
    }

    public double getPerimeter()
    {
        return n * side;
    }

    public double getArea()
    {
        return (n * side) * 5;
    }
}


public class TestRegularPolygon 
{
    public static void main(String[] args) 
    {
        RegularPolygon mypol = new RegularPolygon(6, 4);
        System.out.println("the area is: " + mypol.getArea() + " the perimeter is " + mypol.getPerimeter());

        RegularPolygon yourpol = new RegularPolygon(10, 4, 5.6, 7.8);
        System.out.println("the area is: " + yourpol.getArea() + " the perimeter is " + yourpol.getPerimeter());
    }
}
</code></pre>
