line.java

Java2入门经典第五章源码

package Geometry;

public class Line
{
  // Create a line from two points
  public Line(final Point start, final Point end)
  {
    this.start = new Point(start);
    this.end = new Point(end);
  }

  // Create a line from two coordinate pairs
  public Line(double xStart, double yStart, double xEnd, double yEnd)
  {
    start = new Point(xStart, yStart);       // Create the start point
    end = new Point(xEnd, yEnd);             // Create the end point
  }

  // Calculate the length of a line
  public double length()
  {
    return start.distance(end);              // Use the method from the Point class
  }

  // Return a point as the intersection of two lines -- called from a Line object
  public Point intersects(final Line line1)
  {

    Point localPoint = new Point(0, 0);

    double num = 
      (this.end.getY() - this.start.getY())*(this.start.getX() - line1.start.getX()) -
      (this.end.getX() - this.start.getX())*(this.start.getY() - line1.start.getY());

    double denom = 
      (this.end.getY() - this.start.getY())*(line1.end.getX() - line1.start.getX()) -
      (this.end.getX() - this.start.getX())*(line1.end.getY() - line1.start.getY());

    localPoint.setX(line1.start.getX() + (line1.end.getX() - line1.start.getX())*num/denom);
    localPoint.setY(line1.start.getY() + (line1.end.getY() - line1.start.getY())*num/denom);

    return localPoint;
  }

  // Convert a line to a string 
  public String toString()
  {
    return "(" + start+ "):(" + end + ")";    // As "(start):(end)"
  }                                           // that is, "(x1, y1):(x2, y2)"

  // Data members
  Point start;                               // Start point of line
  Point end;                                 // End point of line
}