/**
 * A line in 2-dimensional space. A line is uniquely determined
 * by 2 points in space.
 * 
 * Illustrates:
 * - A class whose instance variables themselves have class type
 * - Multipe constructors
 *
 */
public class Line{
    private Point p1;
    private Point p2;    
    private double slope;
    
    /**
     * Represents the line that passes through the specified points
     */
    public Line(Point point1, Point point2){
        p1 = point1;
        p2 = point2;        
        slope = (p1.getY() - p2.getY()) / (p1.getX() - p2.getX());
    }
    
    /**
     * Represents the line that passes through the specified points
     */
    public Line(double x1, double y1, double x2, double y2){
        p1 = new Point(x1, y1);
        p2 = new Point(x2, y2);
        slope = (p1.getY() - p2.getY()) / (p1.getX() - p2.getX());        
    }
    
    
    /**
     * Returns back the slope of the line
     */
    public double getSlope(){            
        return slope;
    }
    
    /**
     * Uses the following formula to compute the y-coordinate for a given x-coordinate:
     * 
     *      y - y1 = m * (x - x1)
     * 
     * or, equivalently,
     * 
     *      y = m * (x - x1) + y1
     * 
     * where 
     * 
     *      x is the x-coordinate passed in
     * and
     *      (x1,y1) is one of the two points on the line
     *      
     */
    public double computeY(double x){
        double y = slope*(x - p1.getX()) + p1.getY();
        return y;
    }        
}