Scala, position objects on a circumference - oop

Question

I am trying to populate a circumference with points located at equal intervals. Here is the code (it uses some Processing, but it is not crucial for understanding):
class Circle (x: Float, y: Float, subdivisions: Int, radius: Float) extends WorldObject(x, y) {
def subs = subdivisions
def r = radius
val d = r + r
def makePoints() : List[Glyph] = {
val step = PConstants.TWO_PI / subdivisions
val points = List.make(subdivisions, new Glyph())
for(i <- 0 to subdivisions - 1) {
points(i) position (PApplet.cos(step * i) * r + xPos, PApplet.sin(step * i) * r + yPos)
}
points
}
val points: List[Glyph] = makePoints()
override def draw() {
applet fill 0
applet stroke 255
applet ellipse(x, y, d, d)
applet fill 255
points map(_.update())
}
}
class Glyph(x: Float, y: Float) extends WorldObject(x, y){
def this() = this(0, 0)
override def draw() {
applet ellipse(xPos, yPos, 10, 10)
}
}
object WorldObject {
}
abstract class WorldObject(var xPos: Float, var yPos: Float) {
def this() = this(0, 0)
def x = xPos
def y = yPos
def update() {
draw()
}
def draw()
def position(x: Float, y: Float) {
xPos = x
yPos = y
}
def move(dx: Float, dy: Float) {
xPos += dx
yPos += dy
}
}
The strange result that I get is that all the points are located at a single place. I have experimented with println checks... the checks in the makePoints() method shows everything ok, but checks in the Circle.draw() or even right after the makePoints() show the result as I see it on the screen - all points are located in a single place, right where the last of them is generated, namely x=430.9017 y=204.89435 for a circle positioned at x=400 y=300 and subdivided to 5 points. So somehow they all get collected into the place where the last of them sits.
Why is there such a behavior? What am I doing wrong?
UPD: We have been able to locate the reason, see below:
Answering the question, user unknown changed the code to use the fill method instead of make. The main relevant difference between them is that make pre-computes it's arguments and fill does not. Thus make fills the list with totally identical items. However, fill repeats the computation on each addition. Here are the source codes of these methods from Scala sources:
/** Create a list containing several copies of an element.
*
* #param n the length of the resulting list
* #param elem the element composing the resulting list
* #return a list composed of n elements all equal to elem
*/
#deprecated("use `fill' instead", "2.8.0")
def make[A](n: Int, elem: A): List[A] = {
val b = new ListBuffer[A]
var i = 0
while (i < n) {
b += elem
i += 1
}
b.toList
}
And the fill method:
/** Produces a $coll containing the results of some element computation a number of times.
* #param n the number of elements contained in the $coll.
* #param elem the element computation
* #return A $coll that contains the results of `n` evaluations of `elem`.
*/
def fill[A](n: Int)(elem: => A): CC[A] = {
val b = newBuilder[A]
b.sizeHint(n)
var i = 0
while (i < n) {
b += elem
i += 1
}
b.result
}

Answer 1

I changed a lot of variables forth and back (def x = ... => def x () = , x/ this.x and x/xPos and so on) added println statements and removed (P)applet-stuff, which made the compiler complain.
Providing a compilable, runnable, standalone demo would be beneficial. Here it is:
class Circle (x: Float, y: Float, subdivisions: Int, radius: Float)
extends WorldObject (x, y) {
def subs = subdivisions
def r = radius
val d = r + r
def makePoints() : List[Glyph] = {
// val step = PConstants.TWO_PI / subdivisions
val step = 6.283F / subdivisions
val points = List.fill (subdivisions) (new Glyph ())
for (i <- 0 to subdivisions - 1) {
// points (i) position (PApplet.cos (step * i) * r + xPos,
// PApplet.sin (step * i) * r + yPos)
val xx = (math.cos (step * i) * r).toFloat + xPos
val yy = (math.sin (step * i) * r).toFloat + yPos
println (xx + ": " + yy)
points (i) position (xx, yy)
}
points
}
val points: List [Glyph] = makePoints ()
override def draw () {
/*
applet fill 0
applet stroke 255
applet ellipse(x, y, d, d)
applet fill 255
*/
// println ("Circle:draw () upd-> " + super.x () + "\t" + y () + "\t" + d);
points map (_.update ())
println ("Circle:draw () <-upd " + x + "\t" + y + "\t" + d);
}
}
class Glyph (x: Float, y: Float) extends WorldObject (x, y) {
def this () = this (0, 0)
override def draw() {
// applet ellipse (xPos, yPos, 10, 10)
println ("Glyph:draw (): " + xPos + "\t" + yPos + "\t" + 10);
}
}
object Circle {
def main (as: Array [String]) : Unit = {
val c = new Circle (400, 300, 5, 100)
c.draw ()
}
}
object WorldObject {
}
abstract class WorldObject (var xPos: Float, var yPos: Float) {
def this () = this (0, 0)
def x = xPos
def y = yPos
def update () {
draw ()
}
def draw ()
def position (x: Float, y: Float) {
xPos = x
yPos = y
// println (x + " ?= " + xPos + " ?= " + (this.x ()))
}
def move (dx: Float, dy: Float) {
xPos += dx
yPos += dy
}
}
My result is:
500.0: 300.0
430.9052: 395.1045
319.10266: 358.78452
319.09177: 241.23045
430.8876: 204.88977
Glyph:draw (): 500.0 300.0 10
Glyph:draw (): 430.9052 395.1045 10
Glyph:draw (): 319.10266 358.78452 10
Glyph:draw (): 319.09177 241.23045 10
Glyph:draw (): 430.8876 204.88977 10
Circle:draw () <-upd 400.0 300.0 200.0
Can you spot the difference?
You should create a copy of your code, and stepwise remove code, which isn't necessary to reproduce the error, checking, whether the error is still present. Then you should reach a much smaller problem, or find the error yourself.