Writing Java code for JavaFX Script

When writing Java classes which can be used in JavaFX scripts, three factors have to be considered: how to create a Java object, how to access its members and how to pass parameters between Java and JavaFX.

Creating Java Objects

Creating Java objects from a JavaFX script is fairly simple, as this functionality is already built into the language. To setup a class, which can be instantiated in a JavaFX script, you just have to provide constructors as you would for the usage in Java classes. In Code Sample 1, a class with two constructors is created.

public class MyJavaClass {

    private String property;

    public MyJavaClass() {
        this.property = "Hello World";
    };

    public MyJavaClass(String property) {
         this.property = property;
    };

    public void printProperty() {
        System.out.println(property);
    }
}

Code Sample 1: Definition of MyJavaClass

To create an instance of MyJavaClass in a JavaFX script, simply call its constructor. Notify that the brackets can be omitted, if a constructor without parameters is called.

var o1 = new MyJavaClass;
var o2 = new MyJavaClass("Goodbye World!");

Code Sample 2: Instantiating MyJavaClass in JavaFX Script

Accessing Members

Accessing members of Java objects from a JavaFX script works as it would in a pure Java environment. The access modifiers public, protected and private imply the same restrictions. As you will see in the example about passing parameters, you can also access static members defined in your Java classes. The following lines create an instance of MyJavaClass and call its method printProperty.

var o1 = new MyJavaClass("Goodbye World!");
o1.printProperty();

Code Sample 3: Accessing a member of MyJavaClass in JavaFX Script

Passing Parameters

When it comes to passing parameters, there are four categories of data types to consider. They are listed in the following table.

JavaFX Type	Java Type
Number	double / java.lang.Double
Integer	int / java.lang.Integer
Boolean	boolean / java.lang.Boolean
String	java.lang.String
Java objects
JavaFX objects
Sequences

Passing primitive data types and Java objects is straightforward. The primitive data types Number, Integer, Boolean, and String are mapped to primitive data types or the equivalent objects as shown in the table. In Code Sample 4, a Java class is defined with methods to take these data types and return them.

public class MyLibrary {

    public static double returnDoublePrimitive (double d) {
        return d;
    }
    public static Double returnDoubleObject (Double d) {
        return d; 
    }

    public static int returnIntegerPrimitive (int i)     {
        return i;
    }
    public static Integer returnIntegerObject  (Integer i) {
        return i;
    }

    public static boolean returnBooleanPrimitive (boolean b) {
        return b;
    }
    public static Boolean returnBooleanObject (Boolean b) {
        return b;
    }

    public static String returnString (String s) {
        return s;
    }
}

Code Sample 4: Definition of MyLibrary

The JavaFX script in Code Sample 5 calls the Java-methods. As the code sample shows, it makes no difference to the JavaFX script, if a primitive data type or the corresponding object is needed as a parameter.

var n1: Number = 3.1415;
var n2: Number;
n2 = MyLibrary.returnDoublePrimitive(n1);
n2 = MyLibrary.returnDoubleObject(n1);

var i1: Integer = 42;
var i2: Integer;
i2 = MyLibrary.returnIntegerPrimitive(i1);
i2 = MyLibrary.returnIntegerObject(i1);

var b1: Boolean = true;
var b2: Boolean;
b2 = MyLibrary.returnBooleanPrimitive(b1);
b2 = MyLibrary.returnBooleanObject(b1);

var s1: String = "Passing a String";
var s2: String;
s2 = MyLibrary.returnString(s1);

Code Sample 5: Passing primitive JavaFX data types

When defining a new Java interface, I’d recommended to use only the data types, which are defined in JavaFX. If that is not possible, the data has to be cast. In most cases, this is done implicitly, but in some cases it has to be done explicitly using the methods byteValue(), shortValue(), longValue(), and floatValue(). To pass a char, the method charAt() of the data type String can be used. In Code Sample 6, a Java class is defined which expects these data types.

There also exist two methods doubleValue() and intValue(), which can be used to cast a Number to an Integer and vice versa. These methods can also be used with literals directly, e.g. “42.floatValue()” casts the magic number to a float.

public class MyLibraryCast {

    public static byte returnBytePrimitive (byte b) {
        return b;
    }
    public static Byte returnByteObject    (Byte b) {
        return b;
    }

    public static short returnShortPrimitive (short s) {
        return s;
    }
    public static Short returnShortObject    (Short s) {
        return s;
    }

    public static long returnLongPrimitive (long l) {
        return l;
    }
    public static Long returnLongObject    (Long l) {
        return l;
    }

    public static float returnFloatPrimitive (float f) {
        return f;
    }
    public static Float returnFloatObject    (Float f) {
        return f;
    }

    public static char returnCharacterPrimitive   (char c) {
        return c;
    }
    public static Character returnCharacterObject (Character c) {
        return c;
    }
}

Code Sample 6: Definition of MyLibraryCast

Code sample 7 shows how these methods can be called. In these cases there is a difference between using the primitive data types in Java and using the equivalent objects as you can see in the method-calls below.

var i1: Integer = 42;
var i2: Integer;

i2 = MyLibraryCast.returnBytePrimitive(i1);
i2 = MyLibraryCast.returnByteObject(i1.byteValue());

i2 = MyLibraryCast.returnShortPrimitive(i1);
i2 = MyLibraryCast.returnShortObject(i1.shortValue());

i2 = MyLibraryCast.returnLongPrimitive(i1) as Integer;
i2 = MyLibraryCast.returnLongObject(i1.longValue()).intValue();

var n1: Number = 3.1415;
var n2: Number;

n2 = MyLibraryCast.returnFloatPrimitive(n1.floatValue());
n2 = MyLibraryCast.returnFloatObject(n1.floatValue());

var s1: String = "c";
var s2: String;

s2 = java.lang.Character.toString (MyLibraryCast.returnCharacterPrimitive (s1.charAt(0)) );
s2 = MyLibraryCast.returnCharacterObject(s1.charAt(0)).toString();

Code Sample 7: Passing primitive Java data types by casting

A Java object does not need to be mapped, but is passed as the very same object. In the Java code it makes no difference if the Java object was passed from a JavaFX script or from some other Java code. The static method in Code Sample 8 take an instance of MyJavaClass (see Code Sample 1), calls its method printProperty and returns the object.

public class MyLibraryForObjects {
    public static MyJavaClass printAndReturnMyJavaClass (MyJavaClass o) {
        o.printProperty();
        return o;
    }
}

Code Sample 8: Definition of MyLibraryForObjects

The JavaFX script in Code Sample 9 creates an instance of MyJavaClass, passes it to the method printAndReturnMyJavaClass and saves the result.

var o1: MyJavaClass = new MyJavaClass("Hello Java!");
var o2: MyJavaClass;

o2 = MyLibraryForObjects.printAndReturnMyJavaClass(o1);

Code Sample 9: Passing a Java object

Passing JavaFX objects and sequences to Java is slightly more difficult and will be covered in the next articles.

10 responses to “Writing Java code for JavaFX Script”

Alex

10. April 2008

Hi Mike,

Can you please tell us, what casting is done in your MyLibraryCast class, as each method in it gets and returns a value of same type. AFAIK casting means converting from one type to another, like String to Integer. Is it so ?
Michael Heinrichs

10. April 2008

The name of the library is really badly chosen. Actually I wanted to express, that some casting needs to be done to call the methods of this library. Byte, Short etc. are not primitive datatypes in JavaFX Script. The casting is done in the JavaFX code sample below (e.g. i1.byteValue() to cast an Integer (indirectly) to a Byte).
fabio

16. May 2008

amigo. porque quando eu faço uma classe em java e depois vou instaciar em outro arquivo javafx fica dando erro de compilação dizendo que não esta definida o tipo.
fabio

16. May 2008

amigo. porque quando eu faço uma classe em java e depois vou instanciar em outro arquivo javafx fica dando erro de compilação dizendo que não esta definida o tipo.
Luigi

20. June 2008

hi,
i haved insalled the eclipse pluging and
try this but i cant call the java-class why?
Marko

14. October 2008

Here you deal only with primitive types. What I have is array of objects that I would like to cast into Sequence in order to use it JavaFX. Any help?
Moprano

21. April 2009

Any feedback to Marko’s request? I am in the same boat.
LaoZhang

22. June 2009

Moprano & Marko, i think the better way is just use the Array instead of any collections in your java classes. Then you can simply refer them in your FX script.
rtkrvj

2. September 2009

Hi!

On following code samples 5 and 6, I have created class MyLibrary in the same package and declared methods as :

public static double returnDoublePrimitive (double d) { return d; }
public static Double returnDoubleObject (Double d) { return d; }i am getting

and this in the fx class which is also in the same package,

var n1: Number = 3.1415;
var n2: Number;

n2 = MyLibrary.returnDoublePrimitive(n1);
n2 = MyLibrary.returnDoubleObject(n1);

But the fx file gives this error.

There is a garbled class member definition starting here, I have tried to ignore it. Class members can be ‘var’, ‘def’, ‘function’, ‘init’ or ‘postinit’ only.

please suggest.
davix

30. October 2009

I need the other way around, I mean, seting a javafx instance in a java class

thx

Netopyr GmbH