JavaFX 2 and Scala - Like Milk and Cookies (33rd Degrees)

JavaFX 2.0 and Scala, Like Milk
and Cookies Stephen Chin
Chief Agile
Methodologist, GXS
steveonjava@gmail.com
tweet: @steveonjava

Meet the Presenter

Stephen Chin
> Chief Agile
Methodologist, GXS
Family Man > Java Champion
> Open Source Hacker
 JFXtras
Motorcyclist  ScalaFX
 Visage
> User Group Leader
 Silicon Valley JavaFX User
Group
 Streamed Live!

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.

Programming Languages
> JavaFX Script is no longer supported by Oracle
 Existing JavaFX Script based applications will
continue to run
 Visage is the open-source successor to the JavaFX
Script language
> JavaFX 2.0 APIs are now in Java
 Pure Java APIs for all of JavaFX
 Binding and Sequences exposed as Java APIs
 FXML Markup for tooling

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

Example Application
public class HelloStage extends Application {
@Override public void start(Stage stage) {
stage.setTitle("Hello Stage");
stage.setWidth(600);
stage.setHeight(450);
Group root = new Group();
Scene scene = new Scene(root);
scene.setFill(Color.LIGHTGREEN);
stage.setScene(scene);
stage.show();
}
public static void main(String[] args) {
Application.launch(args);
}
}

Example Application Using Builders
public class HelloStage extends Application {

@Override public void start(Stage stage) {
stage.setTitle("Hello Stage");
stage.setScene(SceneBuilder.create()
.fill(Color.LIGHTGREEN)
.width(600)
.height(450)
.build());
stage.show();
}

}
}

Observable Properties
> Supports watching for changes to
properties
> Implemented via anonymous inner
classes
> Will take advantage of closures in the
future

Observable Pseudo-Properties
final Rectangle rect = new Rectangle();
rect.setX(40);
rect.setY(40);
rect.setWidth(100);
rect.setHeight(200);

rect.hoverProperty().addListener(new ChangeListener<Boolean>() {

});

rect.setX(40); The property we want to watch
rect.setY(40);
rect.setWidth(100);


});

rect.setX(40); Only one listener used with
rect.setY(40); generics to specify the data type
rect.setWidth(100);


});

rect.setX(40);
rect.setY(40);
rect.setWidth(100);

public void changed(ObservableValue<? extends Boolean> property,
Boolean oldValue, Boolean value) {

}
});

Refers to the
Rectangle.hoverProperty()

rect.setX(40);
rect.setY(40);
rect.setWidth(100);

public void changed(ObservableValue<? extends Boolean> property,
Boolean oldValue, Boolean value) {
rect.setFill(rect.isHover() ? Color.GREEN : Color.RED);
}
});

Binding
> Unquestionably the biggest JavaFX
Script innovation
> Supported via a PropertyBinding class
> Lazy invocation for high performance
> Static construction syntax for simple
cases
 e.g.: bind(<property>),
bindBiDirectional(<property>)

Sequences in Java
> Replaced with an Observable List

> Public API is based on JavaFX sequences

> Internal code can use lighter collections API

> JavaFX 2.0 also has an Observable Map

Vanishing Circles

18

Application Skeleton
public class VanishingCircles extends Application {
}
@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);
}

20

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

21

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();
}
});

22

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();

23

JavaFX With Scala

24

What is Scala
2012
2001 2006 • Scala 2.9.1-1
• Scala Started • Scala v2.0 (latest)

2003/2004 2011
• Scala v1.0 • Scala 2.9.1

> Started in 2001 by Martin Odersky
> Compiles to Java bytecodes
> Pure object-oriented language
> Also a functional programming language
25

Why Scala?
> Shares many language features with JavaFX Script
that make GUI programming easier:
 Static Type Checking – Catch your errors at compile
time
 Closures – Wrap behavior and pass it by reference
 Declarative – Express the UI by describing what it
should look like

> Scala also supports Type Safe DSLs!
 Implicit Conversions – type safe class extension
 Operator Overloading – with standard precedence rules

26

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();
}
}

27

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)
}
}
}
}

28

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

29

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

30

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

31

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

32

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"

33

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();
34

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

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

35

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

36

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

37

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

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

38

> Optional arguments for event objects
> 100% type-safe

onMouseClicked = {
}
Compact syntax
{body}
39

> Optional arguments for event objects Optional event
> 100% type-safe parameter
{(event) => body}

onMouseClicked = { (e: MouseEvent) =>
}

40

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.
41

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?!?
42

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.
43

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

44

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.

45

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?
46

@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.

47

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?!?

48

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 49

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
50

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!
52

JavaFX 2 and Scala - Like Milk and Cookies (33rd Degrees)

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