Java FX Intro

FXML applications

FXML layouts can be created easily with the Scene Builder tool, which will create the same FXML file set-up regardless of IDE used. This tool is similar to the idea of a WYSYWIG ("what you see is what you get") editor for web pages.

The JavaFX Application Window

• Controls: These are the GUI components, like text fields, buttons, etc. Similar to the components in the Swing libraries
• Stage: The window in which the JavaFX app's GUI is displayed. class Stage is in the package javafx.stage
• Scene: The stage contains an active scene, defining the GUI as a scene graph -- this is a tree data structure of the visual elements on the app. class Scene is in package javafx.scene
• Nodes: visual elements in the scene graph. The root node is the outermost, typically a container that contains other elements (nodes) inside. Each other node has one parent
• Layout containers: A node that has children is typically a layout container that arranges the child nodes in a scene. Containers can contain other containers!
• Event Handler and Controller Class: A GUI event handler in an FXML GUI is defined in a controller class -- i.e. the class where the event handlers go.

The Application class

• JavaFX applications extend from class Application, in the package javafx.application
• A JavaFX application can be launched from a main program by calling the static method launch(String... args). (Note that this allows a main() function's commmand-line parameters to be sent along into the applciation
• When a JavaFX application is launched:
  • An instance of the specified Application class is created (an object)
  • The init() method is called for that object
  • The start(Stage) method is called for that object
  • The application finishes either when Platform.exit() is called, or when the last window has been closed and the implicitExit attribute on Platform is true
  • The stop() method is called for the object
• Note that this structure is similar to that of an applet, which has four functions used for its core control (init, start, stop, destroy)
• init(), start(), and stop() are all inherited methods that can be overridden. start() is the only one that must be overridden, because it is an abstract method

Format of an application that uses a .fxml file for its GUI layout

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class YaddaYadda extends Application 
{
    
    @Override
    public void start(Stage stage) throws Exception 
    {
        Parent root = 
	     FXMLLoader.load(getClass().getResource("yadda.fxml"));
        
        Scene scene = new Scene(root);	// attach scene graph to scene
        scene.setTitle("Yadda App");    // set the title bar of the window
        stage.setScene(scene);          // attach scene to the stage
        stage.show();                   // display the stage
    }

    public static void main(String[] args) 
    {
        launch(args);    // create a YaddaYadda object and call start
    }
}

Also note that the .fxml file with the GUI items and layout is loaded by the static load() method of class FXMLLoader.

Scene Builder user guide

We will do some demos in class on building some GUI layouts with SceneBuilder