JavaFX - onCloseRequest() overrules my boolean statement

Question

In my GUI for my program, I have a line:

window.setOnCloseRequest(closeProgram());

This is run whenever the user presses the X button on the Window frame (not a button I made, but is default on every single GUI application).

showWarningWindow is a boolean method which shows a confirmation window about closing the program. If true, it will run Platform.exit();

I am 100% sure that my showWarningWindow() method returns false, and yet the application still closes. Why is this and how can I stop it from happening?

/**
 * This method is called when the user wishes to close the program.
 */
private void closeProgram()
{
    if (logic.unsavedChangesExist())
    {
        if (showWarningWindow("You currently have unsaved changes made to the database."
                + "\nAre you sure you would like to exit without saving?"))
        {
            Platform.exit();
        }
    }
}

Answer 1

As in the documentation,

The installed event handler can prevent window closing by consuming the received event.

So you need

window.setOnCloseRequest(event -> closeProgram(event));

and

private void closeProgram(WindowEvent event)
{
    if (logic.unsavedChangesExist())
    {
        if (showWarningWindow("You currently have unsaved changes made to the database."
                + "\nAre you sure you would like to exit without saving?"))
        {
            Platform.exit();
        } else {
            event.consume();
        }
    }
}

Without this, your window will close no matter the return value of showWarningWindow. If it happens to be the last window open, and Platform.isImplicitExit() returns true (the default), then the application will exit.