Point objects?

Question

(copied from an e-book)based from the code below, how come it didn't used a data type when declaring the instance variables?
class Line {
  Point start;   // Start point of line
  Point end;     // End point of line
  // Create a line from two points
  Line(final Point start, final Point end) {
    this.start = new Point(start);
    this.end = new Point(end);
  // Create a line from two coordinate pairs
  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
  double length() {
    return start.distance(end);  // Use the method from the Point class
  // Convert a line to a string
  public String toString() {
    return "(" + start+ "):(" + end + ")";    // As "(start):(end)"
  }                                           // that is, "(x1, y1):(x2, y2)"
}

Answer 1

Point is a class,
hmmn..im just a lil confused about those instance variables
it used a Point class instead of declaring the start and end coordinates as;
double start; //something like this two, hope you got what i mean
double end;