JavaFX Script for Java developers, Part 2

Comfortable arrays

Arrays in JavaFX are easy-to-use and act more like sequences. Here’s one:

var letters = ['A', 'B', 'D'];

Let’s print it,

println(letters);

get its size,

println(sizeof letters);

reverse it,

println(reverse letters);

insert an element at the end,

insert 'E' into letters;
println(letters);

insert more elements at the end,

insert ['F', 'G'] into letters;
println(letters);

and insert something at the middle.

insert 'C' after letters[1];
println(letters);

To delete any element you may specify its value,

delete 'E' from letters;
println(letters);

or index.

delete letters[2];
println(letters);

Finally, you may delete all elements with

delete letters;
println(letters);

Powerful selection

Here’s an array of various numbers.

var numbers = [78, 44, 21, 7, 90, 4, 18];

Let’s print those that are strictly smaller than 10,

println(numbers[n | n < 10]);

Note: | means where and n is an arbitrary variable name according to the developer’s taste.

Here’s how to select the elements between 20 and 50,

println(numbers[n | 20 <= n and n <= 50]);

select only the even elements,

println(numbers[n | n mod 2 == 0]);

a sublist,

println(numbers[2..4]);

and a tail list.

println(numbers[4..]);

Arrays as ranges

Check this out.

var numbers = [1..10];
println(numbers);

To ommit the last value, simply add a <.

var numbers = [1..<10];
println(numbers);

Here are the multiples of 17 up to 100.

var multiples = [0..100][n | n mod 17 == 0];

Alternatively,

var multiples = [0..100 step 17];

Utilities

Such a prominent data structure should be accompanied by a set of utilities. The equivalent of java.util.Arrays is here javafx.util.Sequences.

It provides a rich toolset for searching, sorting, finding the minimum and maximum values. Of course, all this functionality is based on the natural order (Comparable) or a custom order (Comparator).

For example, we’re developing a game.

class Player {
    var name: String;
    var age: Integer;
}

It’s good to provide a proper toString() implementation.

class Player {
    var name: String;
    var age: Integer;
    override function toString(): String {
        return name;
    }
}

Let’s define a natural order. For a player, his age makes sense.

class Player extends Comparable {
    var name: String;
    var age: Integer;
    override function toString(): String {
        return name;
    }
    override function compareTo(other: Object): Integer {
        return age - (other as Player).age;
    }
}

Here are a few of them…

var players = [
    Player {name: 'Madonna' age: 56},
    Player {name: 'Katie Perry' age: 24},
    Player {name: 'Jennifer Lopez'  age: 38}];

Let’s print them,

println(players);

and sort them.

println(Sequences.sort(players));

The powerful selectors do apply here as well.

println(players[p | p.age > 30]);

println(players[p | p.name.startsWith('M')]);

Before moving on, let’s try to modify the Player class a bit.

class Player extends Comparable<Player> {
    var name: String;
    var age: Integer;
    override function compareTo(other: Player): Integer {
        return age - other.age;
    }
}

Compilation fails, because JavaFX does not yet support generic parameters.

Enhanced for loop

The enhanced for loop of Java is here.

for (player in players) {
    player.move();
}

At a first glance, just the keyword in is introduced. But there’s more.

Make statistics out of the players’ ages :

var ages = for (player in players) player.age;
println(ages);

Quickly get a list of the players’ names :

var activePlayers = for (player in players) player.name;
println(activePlayers);

Get their names in capital letters :

var listPlayers = for (player in players) player.name.toUpperCase();
println(listPlayers);

Actually you may get an array from any loop, if the last statement returns something.

var array = for (number in [1..100]) {
    // more statements
    Math.sin(number);
}

Even the following is valid.

var array = for (number in [1..100]) {
    // more statements
    number;
}

This feature is useful for fast graphics transformations.

var cubes = for (number in [1..100]) number * number * number;

As an addition to Java, protection is provided for the parameter; it’s value cannot be altered.

for (number in [1..10]) {
    // compilation fails
    number = number + 2;
}

Strings and formatting

Strings may be declared with single quotes as well. The following initializations are all valid.

var text1 = "Create ";
var text2 = 'richer ';
var text3 = new String("internet ");
var text4 = new String('applications.');

Here’s a complete sentence with some Java chaining,

var sentence = text1.concat(text2).concat(text3).concat(text4);

or a StringBuilder.

sentence = new StringBuilder(text1).append(text2).append(text3).append(text4).toString();

Fortunately, the plus operator for strings is well deprecated.

sentence = text1 + text2 + text3 + text4; // compilation fails

Even better, a new feature is here.

var number = 10;
println("A number: {number}");

What’s between the braces gets evaluated.

var number = 10;
println("It's square: {number * number}");

So these statements in Java,

int amount = 7;
String status = String.format("%d dollars left.", amount);
System.out.format("If only I had %d!\n", 1000 * amount);

in JavaFX would be:

var amount = 7;
var status = "{amount} dollars left.";
println("If only I had {1000 * amount}!");

More examples.

sentence = "{text1}{text2}{text3}{text4}";
println(sentence);

sentence = "Visualise {text2}{text3}{text4}";
println(sentence);

sentence = "Visualise {text2.toUpperCase()}{text3}{text4}";
println(sentence);

sentence = "Visualise {text2.toUpperCase()}{text3}{if (true) 'experiences.' else text4}";
println(sentence);

Wrap up

In JavaFX casting is provided by the "as" keyword. Also, "extends" is used for any IS-A relationship.

class Child extends Parent, Comparable {
    // implementation
}

Consider this small sequence.

var letters = ['A', 'B', 'D'];

JavaFX provides compile-time type safety for arrays. For example, this fragment will not compile successfully.

// assigning an Integer to a String
letters[0] = 100;
// inserting an Integer to a String[]
insert 100 into letters;

On the other hand, JavaFX gracefully handles some common unchecked exceptions. Consider this example:

// exceeding the bounds of an array
println(letters[100]);
delete letters[100];
letters[100] = 'Z';
println("No exception is thrown!");

The last part of this series will focus on two brand-new features of JavaFX Script.

• JavaFX API
• JavaFX Examples
• JavaFX Support in NetBeans

Thank you.

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Possibly related posts: (automatically generated)

• JavaFX Script for Java developers, Part 1

Tags: JavaFX