FXML 2.0 overview

FXML 2.0 is a declarative markup language for JavaFX based on the FXML 1.0 markup language, adding powerful new features:

Compile markup directly to bytecode

FXML 2.0 files are compiled directly to bytecode, and don’t require FXMLLoader to load the documents at runtime. No parsing is required, and no reflection is necessary to instantiate the JavaFX object graph. This dramatically improves the loading performance of FXML files.

Here’s how an FXML 2.0 file is compiled to a Java class:

com/sample/NumberDialog.fxml

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.control.*?>

<VBox xmlns="http://javafx.com/javafx" xmlns:fx="http://jfxcore.org/fxml/2.0">
    <Label text="Enter a number:"/>
    <TextField fx:id="textField"/>
    <Label text="The value cannot be empty" visible="${textField.text.empty}"/>
</VBox>

The resulting class is named com.sample.NumberDialog, corresponding to the name of the FXML file. It extends the javafx.scene.layout.VBox class and its content is similar to the following decompiled code:

com.sample.NumberDialog

// Reconstructed from bytecode, details omitted
public class NumberDialog extends VBox {
    protected TextField textField;

    public NumberDialog() {
        __FX$RuntimeContext var1 = new __FX$RuntimeContext(this, 2);
        TextField var2 = this.textField = new TextField();
        var1.push(this);
        ObservableList var3 = this.getChildren();
        Label var10002 = new Label();
        var10002.setText("Enter a number:");
        var3.add(var10002);
        var2.setId("textField");
        var3.add(var2);
        var10002 = new Label();
        var1.push(var10002);
        var10002.setText("The value cannot be empty");
        StringProperty var4 = (StringProperty)
            ((TextField)((MainView)var1.parents[0]).textField).textProperty();
        Object var10003;
        if (var4 == null) {
            boolean var5 = false;
            var10003 = new __FX$BooleanConstant(var5);
        } else {
            var10003 = new __FX$textField$textProperty$isEmpty(var4);
        }

        Object var6 = var10003;
        var10002.visibleProperty().bind((ObservableValue)var6);
        var1.pop();
        var3.add(var10002);
        var1.pop();
    }
}

In many cases, custom controls or user interfaces require imperative code for additional functionality. FXML 2.0 supports this with an optional code-behind class to combine FXML markup and Java code.

Compile-time type safety

All symbols referenced in an FXML 2.0 file are resolved at compile time. Errors are surfaced early in the build, instead of later at runtime. Compiler diagnostics make it easy to see what went wrong:

NumberDialog.fxml:8: 'textFiel' in NumberDialog cannot be resolved

    <Label text="The value cannot be empty" visible="${textFiel.text.empty}"/>
                                                       ^^^^^^^^

Bring your own pattern

FXML 2.0 does not use the markup/controller pattern as featured in FXML 1.0 with FXMLLoader. Instead, all FXML files compile down to scene graph nodes, optionally including a code-behind class to combine FXML markup with Java code.

Application developers are free to implement their preferred patterns like MVC or MVVM, but this is not a design choice that is imposed by the FXML 2.0 markup language.