import java.awt.Color;

/**

* A polygon that is equiangular (all angles are equal in measure) and

* equilateral (all sides have the same length). It also has a color.

*/

public class RegularPolygon extends DrawablePolygon {

/**

* Constructs a regular polygon, given the number of sides.

*

* @param nsides the number of sides

*/

public RegularPolygon(int nsides) {

this(nsides, 50);

}

/**

* Constructs a regular polygon, given the number of sides and the radius.

*

* @param nsides the number of sides

* @param radius from center to vertex

*/

public RegularPolygon(int nsides, int radius) {

this(nsides, radius, Color.GRAY);

}

/**

* Constructs a regular polygon, given the number of sides, the radius, and

* fill color.

*

* @param nsides the number of sides

* @param radius from center to vertex

* @param color initial fill color

*/

public RegularPolygon(int nsides, int radius, Color color) {

// validate the arguments

if (nsides < 3) {

throw new IllegalArgumentException("invalid nsides");

}

if (radius <= 0) {

throw new IllegalArgumentException("invalid radius");

}

if (color == null) {

throw new NullPointerException("invalid color");

}

// initialize Polygon attributes

this.npoints = nsides;

this.xpoints = new int[nsides];

this.ypoints = new int[nsides];

this.color = color;

// the amount to rotate for each vertex (in radians)

double theta = 2.0 * Math.PI / nsides;

// rotation that makes the polygon right-side up

double rotate = Math.PI / nsides + Math.PI / 2.0;

// compute x and y coordinates, centered at the origin

for (int i = 0; i < nsides; i++) {

double x = radius * Math.cos(i * theta + rotate);

double y = radius * Math.sin(i * theta + rotate);

xpoints[i] = (int) Math.round(x);

ypoints[i] = (int) Math.round(y);

}

}

}