JavaFX FXML Controllers: Constructor or `initialize()` Method – Which One for Initialization?

JavaFX FXML Controller: Constructor vs. Initialize Method

Understanding the Initialization Sequence

When using JavaFX with FXML, understanding the initialization sequence for controllers is crucial. After creating an instance of the controller class specified in the FXML file, the following steps occur:

1. Constructor Invocation: The default constructor of the controller is invoked.
2. FXML Field Population: Any fields in the controller annotated with @FXML are populated with the corresponding components defined in the FXML file.
3. initialize() Method Call: The initialize() method of the controller is executed.

Constructor vs. initialize() Method for Controller Initialization

The constructor and the initialize() method serve distinct purposes in initializing the controller:

• Constructor: The constructor is called first and is responsible for any initialization tasks independent of the FXML component references.
• initialize() Method: The initialize() method is called after the FXML fields have been populated. It provides a suitable opportunity to perform any post-processing or additional initialization that requires access to these components.

Importance of initialize() Method's Access to FXML Fields

The ability of the initialize() method to access the FXML component references is crucial. While the constructor does not have access to these references, the initialize() method can use them to access control properties, set up event listeners, or perform other operations.

Example Usage

In the provided code example, the output demonstrates this behavior:

• The constructor of MainViewController prints "first."
• The initialize() method prints "second."

This sequence illustrates that the initialize() method is called after the FXML fields have been populated and is the appropriate place to use these references for controller initialization.

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