Line.java

Line.java

contents ::

  BasicData.java
  Line.java
  Point.java

/*
    Line.java

    Stewart Fleming
    March 2001

    Implements requirements for measurement system 11.2 Line

    Updated by James Little for cosc 241 exercise 2 8/3/01.
    And again for exercise 2 15/3/01.

  */

package jlittle_ex2;

/**
* Represents a line with the equation Ax + By + C = 0
*/
public class Line {
   /**
       a, b and c represent the line in parametric form.
       Ax + By + c = 0
       This is a more efficient representation for calculations.
       The gradient specified in requirement 11.2.1 is: m = -A/B
    */
    private double a, b, c;

    /** the start and end points of the line */
    Point startPt, endPt;

    /** Construct an empty line */
    Line(){
              a = b = c = 0.0;
    } // end of Line

    /** Construct a line with specific coefficients */
    Line(int xCoeff, int yCoeff, int cOffset) {
        a = xCoeff;
        b = yCoeff;
        c = cOffset;
    } // end of constructor

    /**
     * Construct a line between two points.
     * Requirement 11.2.2
     */
    Line(Point pt1, Point pt2)
    {
        // calculate the coefficients for the line between the points
        a = (double) (pt2.getY() - pt1.getY());
        b = (double) (pt1.getX() - pt2.getX());
        c = (-a * (double) pt1.getX()) - (b * (double) pt1.getY());

        // set the start and end points of the line
        startPt = pt1;
        endPt = pt2;
    } // end of constructor

    /**
     * Indicate if a point lies on the line.
     * Requirement 11.2.7
     */
    public boolean containsPoint(Point pt) {
        return ((a * (double) pt.getX()) + (b * (double) pt.getY()) + c == 0.0);
    } // end containsPoint method

    /**
     * Indicate if this line intersects with the line specified.
     * This line: Ax+ By + C = 0
     * Line1: A'x + B'y + c' = 0
     * The lines do not intersect if AB' - A'B = 0.
     * Otherwise the intersection point is:
     * y = (A'C - AC') / (AB' - A'B)
     * x = (BC' - B'C) / (AB' - A'B)
     * Requirement 11.2.8
     */
    public boolean intersects(Line line1, Point intersectPt) {
        double denom, x, y;

        // nobody appeared to be using denom so I thought I would use it.
        denom = ((a * line1.b) - (line1.a * b));
         // if AB' - A'B = 0, then there is no intercept, and I want to return false
        if(denom!=0.0){
             x = ((b * line1.c) - (line1.b * c)) / ((a * line1.b) - (line1.a * b));
             y = ((line1.a * c) - (a * line1.c)) / ((a * line1.b) - (line1.a * b));
             intersectPt.setX((int) x);
             intersectPt.setY((int) y);
             return true;
         } else
             return false;
    }// end intersects method

    /** Indicates if the line is EXACTLY horizontal */
    public boolean isHorizontal() {
        return (a == 0.0);
    } // end isHorizontal method

    /** Indicates if the line is EXACTLY vertical */
    public boolean isVertical() {
        return (b == 0.0);
    } // end isVertical method
} // end of class Line

James Little