Point.java

/**
 * A point in the Cartesian plane.
 *
 * @author Jim Glenn
 * @version 0.1 1/31/2007
 */

public interface Point
{
    /**
     * Returns the x coordinate of this point.
     *
     * @return the x coordinate of this point
     */

    public double getX();

    /**
     * Returns the y coordinate of this point.
     *
     * @return the y coordinate of this point
     */

    public double getY();

    /**
     * Returns the distance of this point from the origin.
     *
     * @return the distance of this point from the origin
     */

    public double getDistanceFromOrigin();

    /**
     * Returns the angle, in degrees, between the line from this point to the
     * origin and the x-axis.  This point must not be the origin.
     *
     * @return the angle of this point in polar coordinates
     * @throws IllegalStateException if this point is the origin
     */

    public double getAngle();

    /**
     * Moves this pointso that it is the given factor further away from the
     * origin, keeping the (point,origin,x-axis) angle the same.
     *
     * @param factor how much to scale this point by
     */

    public void scale(double factor);
}

XYPoint.java

/**
 * A point in the Cartesian plane.
 *
 * @author Jim Glenn
 * @version 0.1 1/31/2007
 */

public class XYPoint implements Point
{
    /**
     * The x coordinate of this point.
     */

    private double x;

    /**
     * The y coordinate of this point.
     */

    private double y;

    /**
     * Creates a point at the given location in the plane.
     *
     * @param xInit the x coordinate of the new point
     * @param yInit the y coordinate of the new point
     */

    public XYPoint(double initX, double initY)
    {
	x = initX;
	y = initY;
    }

    /**
     * Returns the x coordinate of this point.
     *
     * @return the x coordinate of this point
     */

    public double getX()
    {
	return x;
    }

    /**
     * Returns the y coordinate of this point.
     *
     * @return the y coordinate of this point
     */

    public double getY()
    {
	return y;
    }

    /**
     * Returns the distance of this point from the origin.
     *
     * @return the distance of this point from the origin
     */

    public double getDistanceFromOrigin()
    {
	return Math.sqrt(x * x + y * y);
    }

    /**
     * Returns the angle, in degrees, between the line from this point to the
     * origin and the x-axis.
     *
     * @return the angle of this point in polar coordinates
     */

    public double getAngle()
    {
	if (getDistanceFromOrigin() == 0)
	    throw new IllegalStateException("Can't get angle of origin");

	double angle;

	if (y > 0)
	    angle = Math.toDegrees(Math.acos(x / getDistanceFromOrigin()));
	else
	    angle = -Math.toDegrees(Math.acos(x / getDistanceFromOrigin()));

	return angle;
    }

    /**
     * Moves this point so that it is the given factor further away from the
     * origin, keeping the (point,origin,x-axis) angle the same.
     *
     * @param factor how much to scale this point by
     */

    public void scale(double factor)
    {
	x *= factor;
	y *= factor;
    }

    /**
     * Returns a printable representation of this point.
     *
     * @return a printable representation of this point
     */

    public String toString()
    {
	return "(" + getX() + "," + getY() + ")";
    }
}

PolarPoint.java

/**
 * A point in the Cartesian plane.
 *
 * @author Jim Glenn
 * @version 0.1 1/31/2007
 */

public class PolarPoint implements Point
{
    /**
     * The distance from this point to the origin.
     */

    private double distance;

    /**
     * The angle between this point, the origin, and the x-axis, in radians.
     */

    private double angle;

    /**
     * Creates a point at the given location in the plane.
     *
     * @param xInit the x coordinate of the new point
     * @param yInit the y coordinate of the new point
     */

    public PolarPoint(double initX, double initY)
    {
	distance = Math.sqrt(initX * initX + initY * initY);

	if (distance > 0.0)
	    {
		if (initY > 0)
		    angle = Math.acos(initX / distance);
		else
		    angle = -Math.acos(initX / distance);
	    }
	else
	    angle = 0.0;
    }

    /**
     * Returns the x coordinate of this point.
     *
     * @return the x coordinate of this point
     */

    public double getX()
    {
	return Math.cos(angle) * distance;
    }

    /**
     * Returns the y coordinate of this point.
     *
     * @return the y coordinate of this point
     */

    public double getY()
    {
	return Math.sin(angle) * distance;
    }

    /**
     * Returns the distance of this point from the origin.
     *
     * @return the distance of this point from the origin
     */

    public double getDistanceFromOrigin()
    {
	return distance;
    }

    /**
     * Returns the angle, in degrees, between the line from this point to the
     * origin and the x-axis.  This point must not be the origin.
     *
     * @return the angle of this point in polar coordinates
     * @throws IllegalStateException if this point is the origin
     */

    public double getAngle()
    {
	if (getDistanceFromOrigin() == 0.0)
	    throw new IllegalStateException("Can't get angle of origin");

	return angle;
    }

    /**
     * Moves this point so that it is the given factor further away from the
     * origin, keeping the (point,origin,x-axis) angle the same.
     *
     * @param factor how much to scale this point by
     */

    public void scale(double factor)
    {
	distance *= factor;
    }

    /**
     * Returns a printable representation of this point.
     *
     * @return a printable representation of this point
     */

    public String toString()
    {
	return "(" + getX() + "," + getY() + ")";
    }
}