Line2D.java

package org.drip.zen.geometry;

/*
 * 1) Slope Intercept Form
 * 2) Construction from slope and intercept
 * 3) Construction from 2 Points
 * 4) Construction From Slope and Point
 * 5) Accessors
 * 6) Y from X
 * 7) X From Y
 * 8) Parallel Line
 * 9) Perpendicular Line
 * 10) Intersection Between Lines
 */

public class Line2D {
    private double _m = 0.;
    private double _b = 0.;

    public Line2D (double m, double b)
    {
        _m = m;
        _b = b;
    }

    public Line2D (Point2D p1, Point2D p2)
    {
        double x1 = p1.getX();
        double x2 = p2.getX();
        double y1 = p1.getY();
        double y2 = p2.getY();

        _m = (y2 - y1) / (x2 - x1);

        _b = y2 - _m * x2;
    }

    public Line2D (double m, Point2D p2)
    {
        double x2 = p2.getX();
        double y2 = p2.getY();

        _m = m;
        _b = y2 - _m * x2;
    }

    public double slope()
    {
        return _m;
    }

    public double yIntercept()
    {
        return _b;
    }

    public void show()
    {
        System.out.println ("Slope: " + _m + "; Intercept: " + _b);
    }

    public double YFromX (double x)
    {
        double y = _m * x + _b;
        return y;
    }

    public double XFromY (double y)
    {
        double x = (y - _b) / _m;
        return x;
    }

    public Line2D parallelLineAtPoint (Point2D p)
    {
        Line2D parallelLine = new Line2D (_m, p);

        return parallelLine;
    }

    public Line2D perpendicularLineAtPoint (Point2D p)
    {
        Line2D perpendicularLine = new Line2D (-1 / _m, p);

        return perpendicularLine;
    }

    public Point2D intersection (Line2D lineOther)
    {
        double b1 = yIntercept();
        double b2 = lineOther.yIntercept();
        double m1 = slope();
        double m2 = lineOther.slope();

        double xIntersection = -1 * (b2 - b1) / (m2 - m1);
        double yIntersection = m1 * xIntersection + b1;

        Point2D pointIntersection = new Point2D (xIntersection, yIntersection);

        return pointIntersection;
    }

    public static void main (String[] args)
    {
        double mySlope = 1;
        double myIntercept = 2;

        Line2D myFirstLine = new Line2D (mySlope, myIntercept);

        myFirstLine.show();

        Point2D point1 = new Point2D (1, 3);

        Point2D point2 = new Point2D (4, 6);

        Line2D mySecondLine = new Line2D (point1, point2);

        mySecondLine.show();

        Line2D myThirdLine = new Line2D (mySlope, point2);

        myThirdLine.show();

        double x1 = 1;

        double y1 = myThirdLine.YFromX (x1);

        System.out.println ("Y From  = " + x1 + " is " + y1);

        double y2 = 1;

        double x2 = myThirdLine.XFromY (y2);

        System.out.println ("X From Y = " + y2 + " is " + x2);

        Point2D linePoint = new Point2D (6, 12);

        Line2D parallelLine = myThirdLine.parallelLineAtPoint (linePoint);

        parallelLine.show();

        Line2D perpendicularLine = myThirdLine.parallelLineAtPoint (linePoint);

        perpendicularLine.show();

        Line2D firstLine = new Line2D (new Point2D (0, 0), new Point2D (1, 1));

        Line2D secondLine = new Line2D (new Point2D (1, 1), new Point2D (2, 0));

        Point2D pIntersect = firstLine.intersection (secondLine);

        pIntersect.printCoordinate();
    }
}