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);
}
}
}
