JavaFX and Scala - Like Milk and Cookies

JavaFX and Scala – Like Milk and Cookies
Stephen Chin Luc Duponcheel
JavaFX Evangelist, Oracle Independent, ImagineJ
steveonjava@gmail.com luc.duponcheel@gmail.com
tweet: @steveonjava tweet: @LucDup

Meet the Presenters

Stephen Chin Luc Duponcheel

Family Man

Motorcyclist BeJUG

Researcher

JavaFX 2.0 Platform
Immersive Application Experience
> Cross-platform
Animation, Video, Charting
> Integrate Java, JavaScript, and
HTML5 in the same application
> New graphics stack takes
advantage of hardware
acceleration for 2D and 3D
applications
> Use your favorite IDE:
NetBeans, Eclipse, IntelliJ, etc.

JavaFX in Java
> JavaFX API uses an enhanced JavaBeans
pattern
> Similar in feel to other UI toolkits (Swing,
Pivot, etc.)
> Uses builder pattern to minimize boilerplate

Vanishing Circles

7

Application Skeleton
public class VanishingCircles extends Application {
public static void main(String[] args) {
Application.launch(args);
}
@Override
public void start(Stage primaryStage) {
primaryStage.setTitle("Vanishing Circles");
Group root = new Group();
Scene scene = new Scene(root, 800, 600, Color.BLACK);
[create the circles…]
root.getChildren().addAll(circles);
primaryStage.setScene(scene);
primaryStage.show();
[begin the animation…]
}
}

Create the Circles
List<Circle> circles = new ArrayList<Circle>();
for (int i = 0; i < 50; i++) {
final Circle circle = new Circle(150);
circle.setCenterX(Math.random() * 800);
circle.setCenterY(Math.random() * 600);
circle.setFill(new Color(Math.random(), Math.random(),
Math.random(), .2));
circle.setEffect(new BoxBlur(10, 10, 3));
circle.setStroke(Color.WHITE);
[setup binding…]
[setup event listeners…]
circles.add(circle);
}

9

Setup Binding
circle.strokeWidthProperty().bind(Bindings
.when(circle.hoverProperty())
.then(4)
.otherwise(0)
);

10

Setup Event Listeners
circle.addEventHandler(MouseEvent.MOUSE_CLICKED,
new EventHandler<MouseEvent>() {
public void handle(MouseEvent t) {
KeyValue collapse = new KeyValue(circle.radiusProperty(), 0);
new Timeline(new KeyFrame(Duration.seconds(3),
collapse)).play();
}
});

11

Begin the Animation
Timeline moveCircles = new Timeline();
for (Circle circle : circles) {
KeyValue moveX = new KeyValue(circle.centerXProperty(),
Math.random() * 800);
KeyValue moveY = new KeyValue(circle.centerYProperty(),
Math.random() * 600);
moveCircles.getKeyFrames().add(new KeyFrame(Duration.seconds(40),
moveX, moveY));
}
moveCircles.play();

12

JavaFX With Scala

13

Java vs. Scala DSL
public class VanishingCircles extends Application { object VanishingCircles extends JFXApp {
var circles: Seq[Circle] = null
public static void main(String[] args) { stage = new Stage {
Application.launch(args); title = "Vanishing Circles"
} width = 800
height = 600
@Override scene = new Scene {
public void start(Stage primaryStage) { fill = BLACK
primaryStage.setTitle("Vanishing Circles"); circles = for (i <- 0 until 50) yield new Circle {
Group root = new Group(); centerX = random * 800
Scene scene = new Scene(root, 800, 600, Color.BLACK); centerY = random * 600
List<Circle> circles = new ArrayList<Circle>(); radius = 150
for (int i = 0; i < 50; i++) { fill = color(random, random, random, .2)
final Circle circle = new Circle(150); effect = new BoxBlur(10, 10, 3)

40 Lines
circle.setCenterX(Math.random() * 800);
circle.setCenterY(Math.random() * 600);
circle.setFill(new Color(Math.random(), Math.random(), Math.random(), .2));
circle.setEffect(new BoxBlur(10, 10, 3));
33 Lines
strokeWidth <== when (hover) then 4 otherwise 0
stroke = WHITE
onMouseClicked = {
Timeline(at (3 s) {radius -> 0}).play()

1299 Characters
circle.addEventHandler(MouseEvent.MOUSE_CLICKED, new
EventHandler<MouseEvent>() {
public void handle(MouseEvent t) {
KeyValue collapse = new KeyValue(circle.radiusProperty(), 0); }
}
}
591 Characters
content = circles

new Timeline(new KeyFrame(Duration.seconds(3), collapse)).play(); }
}
}); new Timeline {
circle.setStroke(Color.WHITE); cycleCount = INDEFINITE
circle.strokeWidthProperty().bind(Bindings.when(circle.hoverProperty()) autoReverse = true
.then(4) keyFrames = for (circle <- circles) yield at (40 s) {
.otherwise(0)); Set(
circles.add(circle); circle.centerX -> random * stage.width,
} circle.centerY -> random * stage.height
root.getChildren().addAll(circles); )
primaryStage.setScene(scene); }
primaryStage.show(); }.play();
}
Timeline moveCircles = new Timeline();
for (Circle circle : circles) {
KeyValue moveX = new KeyValue(circle.centerXProperty(), Math.random() *
800);
KeyValue moveY = new KeyValue(circle.centerYProperty(), Math.random() *
600);
moveCircles.getKeyFrames().add(new KeyFrame(Duration.seconds(40), moveX,
moveY));
}
moveCircles.play();
}
}

14

object VanishingCircles extends JFXApp {
stage = new Stage {
title = "Disappearing Circles"
width = 800
height = 600
scene = new Scene {
fill = BLACK
content = for (i <- 0 until 50) yield new Circle {
centerX = random * 800
centerY = random * 600
radius = 150
fill = color(random, random, random, 0.2)
effect = new BoxBlur(10, 10, 3)
}
}
}
}

15

stage = new Stage {
width = 800
height = 600 class for JavaFX
Base
applications
scene = new Scene {
fill = BLACK
radius = 150
}
}
}
}

16

stage = new Stage {
width = 800
height = 600 Declarative Stage
scene = new Scene {
fill = BLACK
definition
radius = 150
}
}
}
}

17

stage = new Stage {
width = 800
Inline property
height = 600 definitions
scene = new Scene {
fill = BLACK
radius = 150
}
}
}
}

18

stage = new Stage {
width = 800 Sequence Creation Via
height = 600 Loop
scene = new Scene {
fill = BLACK
radius = 150
}
}
}
}

19

Binding in Scala
Infix Addition/Subtraction/Multiplication/Division:
height <== rect1.height + rect2.height
Aggregate Operators:
width <== max(rect1.width, rect2.width,
rect3.width)
Conditional Expressions:
strokeWidth <== when (hover) then 4 otherwise 0
Compound Expressions:
text <== when (rect.hover || circle.hover &&
!disabled) then textField.text + " is enabled"
otherwise "disabled"

20

Animation in Scala
val timeline = new Timeline {
cycleCount = INDEFINITE
autoReverse = true
keyFrames = for (circle <- circles) yield
at (40 s) {
Set(
circle.centerX -> random * stage.width,
circle.centerY -> random * stage.height
)
}
}
timeline.play();
21

JavaFX Script-like animation
Animation in Scala syntax: at (duration) {keyframes}

autoReverse = true
keyFrames = for (circle <- circles) yield at (40 s) {
Set(
)
}
}
timeline.play();

22

Animation in Scala
autoReverse = true
Set(
)
}
}
timeline.play();
Operator overloading for
animation syntax

23

Animation in Scala
autoReverse = true
Set(
circle.centerX -> random * stage.width tween EASE_BOTH,
circle.centerY -> random * stage.height tween EASE_IN
)
}
}
timeline.play();
Optional
tween syntax

24

Event Listeners in Scala
> Supported using the built-in Closure syntax
> Arguments for event objects
> 100% type-safe

onMouseClicked = { (e: MouseEvent) =>
Timeline(at(3 s){radius->0}).play()
}

25

Event Listeners in Scala
> Supported using the built-in Closure syntax
> Arguments for event objects Optional event
> 100% type-safe parameter
{(event) => body}

onMouseClicked = { (e: MouseEvent) =>
Timeline(at(3 s){radius->0}).play()
}

26

Jumping Frogs Puzzle

Image by renwest: http://www.flickr.com/photos/19941963@N00/438340463
27

Jumping Frogs Puzzle
> My first ScalaFX program
> Similar to (but more concise as) my version using
JavaFX 1.2
> After a few JavaFX 1.2 to ScalaFX translation
iterations it just worked
> After some MVC rethinking and a few refactoring
iterations it worked even better (e.g. it is possible
to click on a jumping frog)

28

Application
object JumpingFrogsPuzzle extends JFXApp {
stage = new Stage {
title = TITLE
scene = new Scene {
content =
theShapes.canvasShape ::
theShapes.stoneShapes :::
theView.frogShapes
}
}
}
29

Frog
trait Frog {
def movesToRight: Boolean
def movesToLeft: Boolean
}
class LeftFrog() extends Frog {
def movesToRight = true
def movesToLeft = false
}
class RightFrog() extends Frog {
def movesToRight = false
def movesToLeft = true
}

30

Model (frogMap)
var frogMap: Map[Int, Frog] = _

private val frogAtPosition = (i: Int) =>
frogMap(i)

val positionOf = (frog: Frog) => (for {
(i, `frog`) <- frogMap
} yield i) head

31

Model (move)
private val move =
(next: Int => Int) => (frog: Frog) =>
frogMap = (for {
entry@(_, aFrog) <- frogMap
if (aFrog != frog)
} yield {
entry
}) + (next(positionOf(frog)) -> frog)

32

View (jump)
private val jump =
(length: Int) =>
(direction: (Double, Double) => Double) =>
(frogShape: FrogShape) => {
// ...
Timeline(Seq(
at(midTime) { frogShape.centerX -> midCenterX
},
at(midTime) { frogShape.centerY -> midCenterY
},
at(endTime) { frogShape.centerX -> endCenterX
},
at(endTime) { frogShape.centerY -> endCenterY }
)).play()
}

33

View (control)
private val control: Unit => Unit = { _ =>
view.frogShapes.foreach {
frogShape => frogShape.onMouseClicked = {
(_: MouseEvent) =>
val frog = frogShape.frog
if (model.canMoveOneRight(frog)) {
view.jumpOneRight(frogShape)
model.moveOneRight(frog)
} else if (model.canMoveTwoRight(frog)) {
view.jumpTwoRight(frogShape)
model.moveTwoRight(frog)
34

ScalaFX Internals
a.k.a. How to Write Your Own Scala DSL

With quotes from Stephen Colebourne (@jodastephen) to help
us keep our sanity!
Disclaimer: Statements taken from http://blog.joda.org and may not accurately reflect his opinion or viewpoint.
35

Application Initialization
> JavaFX Requires all UI code executed on the
Application Thread
> But our ScalaFX Application has no start method:

stage = new Stage {
…
}
}

How Does This Code Work?!?
36

DelayedInit
> Introduced in Scala 2.9
> How to Use It:
1. Extend a special trait called DelayedInit
2. Implement a method of type:
 def delayedInit(x: => Unit): Unit
3. Store off the init closure and call it on the
Application Thread

Joda says…

For me, Scala didn't throw enough away and added too much - a lethal
combination.
37

Hierarchical Implicit Conversions
> ScalaFX defines a set of proxies that mirror the
JavaFX hierarchy
> JavaFX classes are "implicitly" wrapped when you
call a ScalaFX API
> But Scala implicit priority ignores type hierarchy!

JFXNode SFXNode

JFXShape ? SFXShape

JFXCircle ! SFXCircle

38

N-Level Implicit Precedence
> Scala throws an exception if two implicits have the
same precedence
> Classes that are extended have 1 lower
precedence:
object HighPriorityIncludes extends LowerPriorityIncludes {…}
trait LowerPriorityIncludes {…}

> You can stack extended traits n-levels deep to
reduce precision by n
Joda says…

Well, it may be type safe, but its also silent and very deadly.

39

Properties
> JavaFX supports properties of type Boolean,
Integer, Long, Float, Double, String, and Object
> Properties use Generics for type safety
> But generics don't support primitives…

> JavaFX solves this with 20 interfaces and 44
classes for all the type/readable/writable
combinations.

> Can we do better?
40

@specialized
> Special annotation that generates primitive
variants of the class
> Improves performance by avoiding
boxing/unboxing
trait ObservableValue[@specialized(Int, Long,
Float, Double, Boolean) T, J]
> Cuts down on code duplication (ScalaFX only has
18 property/value classes total)
Joda says…

Whatever the problem, the type system is bound to be part of the solution.

41

Bindings
> How does Scala know what order to evaluate this
in?

text <== when (rect.hover || circle.hover
&& !disabled) then textField.text + " is
enabled" otherwise "disabled

And why the funky bind operator?!?

42

Operator Precedence Rules
> First Character Determines Precedence
Lowest Precedence
10. (all letters) Exception Assignment
9. |
Operators, which are
8. ^ even lower…
7. &
6. < > 11. Assignment Operators
5. = !
end with equal
4. :
> But don't start with equal
3. + *
> And cannot be one of:
 <=
2. / %
 >=
1. (all other special
 !=
characters)
Highest Precedence 43

Operator Precedence

text <== when (rect.hover || circle.hover
11 10 9

&& !disabled) then textField.text + " is
7 5 10 3

enabled" otherwise "disabled"
10

Joda says…

Personally, I find the goal of the open and flexible syntax (arbitrary DSLs) to
be not worth the pain
44

Conclusion
> You can use Scala and JavaFX together.
> ScalaFX provides cleaner APIs that are tailor
designed for Scala.
> Try using ScalaFX today and help contribute APIs
for our upcoming 1.0 release!

http://code.google.com/p/scalafx/

Stephen Chin
steveonjava@gmail.com
tweet: @steveonjava

Pro JavaFX 2 Platform Available Now!
46

JavaFX and Scala - Like Milk and Cookies

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