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FXML – The JavaFX Markup Language

We can create JavaFX applications using standard Java programming techniques such as creating

instances of JavaFX objects and linking them together in code. However, an alternative technique

is available to us which we will shortly see has a wealth of power. Since a Scene Graph is a

hierarchical description of nodes what we can do is express this relationship within an XML

document. Such a document used to describe a JavaFX application is called an "FXML" file.

FXML files allow one to describe the relationship between UI nodes in a declarative as opposed to

programmatic fashion. Instead of coding node after node within a Java class, we can describe the

nodes in the FXML file and have JavaFX interpret that XML file for us at runtime. Parsing the file,

JavaFX will construct the corresponding Scene Graph as though we had coded it in Java.

Another important feature of FXML is that a freely available application called "Scene Builder" can

be downloaded off the web. This application allows one to visually compose what the UI will look

like. The input and output of Scene Builder is an FXML file. This means that the construction of

JavaFX UIs just became tremendously easier.

When we write a normal Java application that codes the construction of the nodes by hand, we are

free to intermix arbitrary controller logic. For example, if we define a button then at the same place

we can define an action to be performed when the button is pressed. When we are describing a

scene graph in FXML we don't have that option. This is where we can utilize a class that we will

consider to be our "Controller Class".

A controller class is a standard Java Bean class with fields corresponding to selected nodes within

the graph. Methods in the controller class can also be defined as invokable when certain events

happen in the UI.

Withing Java, we can parse the FXML document to create the tree of nodes using the static method

"FXMLLoader.load()". For example, to load an FXML file located beside the current class we

could code:

Parent root = FXMLLoader.load(getClass().getResource("MyFXML.fxml"));

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