Introduction to the JavaFX™ Script Programming Language

Richard BairStuart MarksSun Microsystems, Inc.

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Richard Bair and Stuart Marks are on the engineering team responsible for the JavaFX

runtime and core class libraries.

Introduction to JavaFX Script Programming

> Major focus: application programming> Minor focus: class and library programming> Not covered:

• finer points of language design• compilation• grammar and syntax• type theory

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> Object-oriented (of course)> Expression language> Declarative and Procedural> Integrates with Java (can import Java classes)> Incorporates the concept of time

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The JavaFX™ Script Language

A scripting language for interactive graphics, media, and animation.

The JavaFX™ Script Language

> Script-like features (type inference, loose exprs)> Convenient data binding> Functions, function variables, anonymous functions> Object model

• Classes, mixins• Instances accessed via references• References can be null...• But NullPointerException isnʼt thrown

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The Flavor of JavaFX Script

> Has sort-of a “scripty” feel to it• Expressions at script level (outside of classes)• Need not declare all types• Object and function literals

> But...• Strongly typed• Still have compile-edit-debug cycle (for now)• Need to declare all variables

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Hello World

> Complete source code:

println("Hello, world!");

> No imports, class declarations, main(), ....> But more complex programs will require them

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> JavaFX Script source files are called “scripts”> Most things in JavaFX Script are expressions

• All blocks are expressions• The last line is the result

• “Statements” are also expressions• x = if (condition) then 1 else 2;

• Function return value• The last expression in function body is the result

> Scripts also contain class declarations

JavaFX Script Explained

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Type Inference

> Neednʼt declare types if the compiler can figure them out• var x = 5; // Integer• var cond = true; // Boolean• function f() { "xyz" } // String

> Statically typed (not dynamic)• Every variable has a type, even if type not declared• Declaration: var varname:type = init-value;• var x:Integer = 5;

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> Primitive types from Java:• Boolean, Integer, Long, String, ...

> Number> Duration> Primitives cannot be null

• Null string coerced to an empty string> Void (only as return “type” of a function)

Data Types

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> Most of the usual suspects, some spelled differently• + - / *• ++ --• *= /= += -=• and or not• = == !=• mod

> But no bitwise operators

Operators

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> if (booleanExpression) then a else b> if (booleanExpression) a else b> if (booleanExpression) { a } else { b }> while (booleanExpression) { ... }> for (i in sequence) { ... }

• Can get index of item “i” by “indexof i”> break, continue, return> try, catch, finally, throw

Flow Control

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Other Language Features

> Comments: // and /* ... */> String expressions:

• println("The value of x is {x}");> Variable declarations

• Use var or def• A def variable cannot be assigned to• But def is not a constant• Can still change value if bind is used

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Sequences

> An immutable, ordered collection of objects> Sequences are flat (they do not nest)> A sequence cannot be null (but it can be empty)> Access by index or by slice> Can insert and delete by value or by index> Single object converted into a sequence if required

• You can sometimes leave off brackets> Sequences of numbers are handled specially

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Sequences

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// the following are equivalentvar names:String[] = "Richard";var names:String[] = [ "Richard" ];

// no null sequences, just empty onesvar names:String[] = null;insert "Fred" into names; // works

// elements are accessed by index or slicevar names = ["Stuart", "Richard", "Jasper"];var jasper = names[2]; // Stringvar speakers = names[0..1]; // String[]

Sequence Operations

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// Insertioninsert [ "Fred", "Jasper" ] into names; // appendsinsert "Stuart" before names[1];insert "Duke" after names[1];

// Deletiondelete "Duke" from names;delete names[0];delete names[x..y];

// Sequences are immutablevar myCopy = names;delete "Richard" from names; // myCopy is unchanged

Sequences

// sequences are flatvar a = [ 1, 2, 3 ];insert [ 4, 5, 6 ] into a;

[ 1, 2, 3, 4, 5, 6 ]

// numeric ranges stored in compact form; useful with for-loops

var b = [1..1000000000];

for (i in [-5000000..5000000]) { ... }

// range expressionsfor (j in [ 0..<10 step 2 ]) { j }

[ 0, 2, 4, 6, 8 ]

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Sequence Selection, Reversal, For-Loop

var seq = [1..10];

println(seq[x | x mod 2 == 0]);[ 2, 4, 6, 8, 10 ]

println(reverse seq);[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

// value of a for-loop is a sequence of values from its bodyprintln(for (x in [1..5]) { x*x });

[ 1, 4, 9, 16, 25 ]

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Classes, Mixins, and APIs

> Normal classes similar to Java classes> Mixin classes like Java interfaces

• Can include function implementations• Can include variable declarations and init values

> Extending classes• At most one normal superclass• Arbitrary number of mixin classes

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Class and Mixin Class Examples

class A {var x;function f() { ... }

}

mixin class M {var y;function g() { ... }

}

class B extends A, M {...

}

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Access Modifiers

> public, protected same as Java> package access must be declared explicitly> The default is now private; no “private” keyword> New modifiers for variable declarations:

• public-read• public-init

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Functions and Function Variables

> Functions• Script level, class, or literal (anonymous)• Return value is last expression in body

> Function variables• A variable that “points to” a function• Can be assigned a function by name or a function

literal

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Function Examples

function sum(seq:Number[]):Number {var s:Number = 0;for (n in seq) { s += n; }s

}

function foo() { println("foo"); }var myFunc = foo;myFunc = function() { println("bar"); }myFunc();

Group {onMouseMoved: function(...) { ... }content: [ ... ]

}

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> bind is a way to tie the value of one variable to the value of an expression• the variable is automatically updated when any

value in the expression changes> Binding must be defined when the variable is

initialized• In initial declaration or in object literal

> Bound variables cannot be set manually> Triggers: code executed when a var changes

Bind and Triggers

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Using Bind

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public class C {public var x1:Number;public var x2:Number;

// Whenever x2 or x1 changes, distance will be updated// Binding can be used to maintain invariants

public-read var distance:Number = bind x2 - x1;}

var d:C = ... ;

d.distance = 100; // error

Bind Performs Minimal Re-evaluation

function f() { ... }function g() { ... }

var a = ... ;var b = ... ;

def x = bind f(a) + g(b)// f and g are called to compute x initially

a++;// to recompute x, f() is called but g() is not!// the return values of function calls are cached

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Triggers

> Allow code to be executed when a variable changes value

> Variable declarations have “on replace” clause> Can access old and new values> Also supports replacement of sequence slices

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Triggers

var a:Number on replace {println("a is now {a}");

}

var b:Number on replace oldB {println("b changed from {oldB} to {b}");

}

var seq:String[] on replace oldItems[start..end] = newItems {println("{seq[start..end]} replaced by {newitems}");

}

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> Concise declarative syntax for object creation> Similar to JavaScript> A series of variable: initial-value pairs> The initial-value is an expression> Can be nested arbitrarily

• Useful for creating scene graph structures> Combine with bind for maximum effect

Object Literals

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Object Literals

// creates a Rectanglevar rect = Rectangle {

x: 10y: 10width: 100height: 100

};rect.x = 20; // ok

// public-init variables can be initialized but not assignedvar p = Point2D {

x: 20y: 30

};p.x = 40; // error

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Nesting Object Literals

// a Rectangle with a Color inside itvar rect = Rectangle {

x: 10y: 10width: 100height: 100fill: Color {

red: 1green: 0blue: 0

}}

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Object Literals

// A variation that allows me to reference the color latervar color:Color; var rect = Rectangle {

x: 10 y: 10 width: 100 height: 100fill: color = Color {

red: 1green: 0blue: 0

}}

var rect2 = Rectangle {x: 200 y: 10 width: 100 height: 100fill: color

}

Bind vs Object Literals

// mutates r1.width if myWidth changesvar r1 = Rectangle {

x: 50y: 50width: bind myWidthheight: 100

}

// creates a new Rectangle, replacing r2, when myWidth changesvar r2 = bind Rectangle {

x: 50y: 50width: myWidthheight: 100

}

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API Design Style

> No getters• Use public-read variables

> No setters• Use public variables with a trigger

> No constructors• Use public-init variables and object literals

> Fewer listeners and callbacks• Expose state variables, allow binding on them

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Time and Duration

> New primitive type: Duration• var d = 100ms;• other units supported: 5s 1m 0.5h

> Timeline class• modifies a value over time toward a target value• supported by special language syntax

• var v = 0;• Timeline { keyFrames: at (1s) { v => 100 } }

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Putting It All Together

> Language and runtime work together> Language

• data binding• object literals• concise syntax

> Runtime and library APIs• scene graph• time & animation

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Putting It All Together

var rotateValue = 0.0;

Timeline { keyFrames: at (4s) { rotateValue => 360.0 } repeatCount: Timeline.INDEFINITE}.play();

Stage { scene: Scene { width: 500 height: 500 content: for (xval in [100, 200, 300], yval in [100, 200, 300]) { Rectangle { x: xval width: 50 y: yval height: 50 rotate: bind rotateValue }} } }

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Putting It All Together – DEMO

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Why A New Language?

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> A programming language is not about telling the computer what to do, but instead is about expressing the programmerʼs intent.

> A programming language needs to embody new, higher-level concepts and to abstract away irrelevant detail. (Brooks 1993, HOPL-II keynote)

> Itʼs fun!

References

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> Part 2: TS-5577 JavaFX Graphics & Animation> Many other JavaFX talks at JavaOne> JavaFX home page: javafx.com

• Tutorials, FAQ, API Documentation• Sample code• Download NetBeans + JavaFX SDK

> JavaFX Script Language Reference• https://openjfx.dev.java.net/langref/

Richard Bairrichard.bair@sun.com

Stuart Marksstuart.marks@sun.com