Is this a bug or a simple Newbie mistake?

Question

Hi.
I'm brand new to JavaFX, so I'm probably misunderstanding something. I've searched the web looking for information concerning it, but since it involves the 'new' operator, it's hard to filter down.
Anyhow, here is the problem:
I'm getting different results when I instantiate an object
using the 'new' operator vs. the declaring it the more
accepted JavaFX way.
This is how I found the "problem".
In order to learn how to program in JavaFX, I found a simple game from the Internet, "Blasteroids", to look at (http://www.remwebdevelopment.com/dev/a41/Programming-Games-in-JavaFX-Part-1.html). I copied and pasted this into:
NetBeans IDE 6.9 (Build 201006101454)
JavaFX 1.3 and got the game to work.
In playing around with it, I converted instantiating an object from the "normal" way:
    var a: Asteroid = Asteroid
        type: type
        posX: x
        posY: y
        moveAngle: moveAngle
        velocityX: Math.sin(Math.toRadians(moveAngle))
            * randomVelocity
        velocityY: -Math.cos(Math.toRadians(moveAngle))
            * randomVelocity
        rotation_increment: rotation_increment
        active: true;
        return a;To using the "new" operator:
        var a:Asteroid = new Asteroid();
        a.type = type;
        a.posX = x;
        a.posY = y;
        a.moveAngle = moveAngle;
        a.velocityX = Math.sin(Math.toRadians(moveAngle)) * randomVelocity;
        a.velocityY = -Math.cos(Math.toRadians(moveAngle))* randomVelocity;
        a.rotation_increment = rotation_increment;
        a.active = true;
        return a;This is the only changes I made. I would "toggle" back and forth between the two, and I would always get the same results.
When I did this conversion, the ship would show up, but the asteroids were gone. Actually, I think they were invisible because every once and a while, my ship would "blow up" and get reset to it's starting position. I tried adding:
a.visible = true;
But that didn't help.
Indecently, I did the same thing with defining the "Stage" using a new operator, and got differing results:
1. the window would open in the bottom right of my screen (vs filling up
most of my screen. I would have to drag it up to play.
2. it had a regular windows border with the minimize, maximize, close
buttons in the top right (vs. a non-movable, border less window with no
maximize, minimize, close buttons.)
Is this a bug, or am I doing something wrong?
Thank you

Answer 1

I suspect you've run into bugs in the Blasteroids program and possibly in Stage in the JavaFX runtime.
For simple cases one would think there should be no difference between this:
var so = SomeObject {
    a: 1
    b: 2
    c: 3
}and this:
var so = SomeObject { }; // or var so = new SomeObject();
so.a = 1;
so.b = 2;
so.c = 3;However, these cases do run through different code paths. In the first case, the init-block of SomeObject sees all the values provided by the caller. In the second case, the triggers on the a, b, and c variables would have to modify the internal state of the object appropriately. If the object has a lot of complex state, the result at the end of setting the three variables (and running their triggers) might not be identical to the object literal after initialization. This is most likely a bug. If an object isn't prepared to have its state variables modified after initialization, it should make them public-init instead of public.
Depending on the object, though, initializing things via an object literal vs. setting variables after initialization might actually have different semantics. This seems to be the case with Stage. The Stage's size is established by its contents at initialization time, and its location at initialization time is determined by using its contents' size and the screen size to center the Stage on the screen. If you create the Stage empty, and then later add contents, the sizing/centering calculations will be based on an empty Stage and will thus give a different result.
Using the object literal technique is idiomatic JavaFX Script, and it's probably more efficient than setting variables after initialization, so I'd recommend sticking with object literals.