Concrete Point No. 2

Abstract Point | Point No. 1 | Point No. 2

In “Concrete Point No. 1” we extended abstract notions of a point that were presented in “An Abstract Point” into concrete JavaScript and Java classes that model a point in one-dimensional space. In this post we continue the pattern by extending those classes with corresponding models of a point in two-dimensional space!

A JavaScript description of a point in two-dimensional space

Given:

// A class that models an abstract point
function Point() {};
Point.prototype = {
  constructor: Point,
  distanceFromOrigin: function() {
    throw new Error("Not implemented");
  },
};

// A class that models a point in one dimension
function PointOnALine(x) {
  Point.call(this);
  this.x = x;
};
PointOnALine.prototype = Object.create(Point.prototype);
PointOnALine.prototype.constructor = PointOnALine;
PointOnALine.prototype.distanceFromOrigin = function() {
  return Math.sqrt(Math.pow(this.x, 2));
};

We can compose:

// A class that models a point in two dimensions
function PointInAPlane(x, y) {
  PointOnALine.call(this, x);
  this.y = y;
};
PointInAPlane.prototype = Object.create(PointOnALine.prototype);
PointInAPlane.prototype.constructor = PointInAPlane;
PointInAPlane.prototype.distanceFromOrigin = function() {
  return Math.sqrt(Math.pow(this.x, 2) + Math.pow(this.y, 2));
};

And then we can do things like:

A Java description of a point in two-dimensional space

Given:

// A class that models an abstract point
abstract class Point {
  Point() {
  }
  abstract double distanceFromOrigin();
}

// A class that models a point in one-dimensional space
class PointOnALine extends Point {
  double x;
  PointOnALine(double x) {
    super();
    this.x = x;
  }
  double distanceFromOrigin() {
    return Math.sqrt(Math.pow(this.x, 2));
  }
}

We can compose:

// A class that models a point in two-dimensional space
class PointInAPlane extends PointOnALine {
  double y;
  PointInAPlane(double x, double y) {
    super(x);
    this.y = y;
  }
  double distanceFromOrigin() {
    return Math.sqrt(Math.pow(this.x, 2) + Math.pow(this.y, 2));
  }
}

And then we can compose code that uses our classes. For example:

class TestPoint {
  public static void main(String[] args) {
    Point p1 = new PointInAPlane(3, 4);
    Point p2 = new PointInAPlane(4, 5);
    System.out.println(p1.distanceFromOrigin());
    System.out.println(p2.distanceFromOrigin());
  }
}

Finally, we can compile and interpret our code!

Abstract Point | Point No. 1 | Point No. 2