code: public void set(double x1, double y1, double x2, double y2)
      {
          this.x1 = x1;
          this.y1 = y1;
          this.x2 = x2;
          this.y2 = y2;
      }
docs: Set the line coordinates.
  
  @param x1 The x coordinate of the start point
  @param y1 The y coordinate of the start point
  @param x2 The x coordinate of the end point
  @param y2 The y coordinate of the end point