JavaFX FXML Controller: Constructor vs. `initialize()` Method – When Should I Use Which?

JavaFX FXML Controller: Understanding the Distinction Between Constructor and Initialize Method

In JavaFX, an FXML controller is responsible for providing the logic behind an FXML file. While the constructor and initialize() method serve similar purposes in initializing the controller, they have distinct characteristics that impact when and how the controller is configured.

The constructor is invoked first during the controller initialization process. It is used to set up any necessary fields or perform tasks that do not require references to FXML-defined components. However, since @FXML-annotated fields are not yet populated at this point, the constructor cannot interact with them.

In contrast, the initialize() method is called after @FXML-annotated fields have been populated. This means that it can access and manipulate components defined in the FXML file. This is the recommended approach for initializing components and performing tasks that rely on their presence.

To illustrate the difference, consider the following example:

public class MainViewController {

    private Button myButton;

    public MainViewController() {
        System.out.println("first");
    }

    @FXML
    public void initialize() {
        System.out.println("second");
        setDisableMyButton();
    }

    private void setDisableMyButton() {
        myButton.setDisable(true);
    }
}

In this example, the constructor simply prints "first," while the initialize() method prints "second" and then disables the "myButton" component. The output would be:

first
second

By using the initialize() method to manipulate @FXML-annotated components, you ensure that the components have been properly initialized before you interact with them. This helps ensure the consistency and reliability of your code.

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