Program is an Application

• Your program should extend javafx.application.Application
• In main, call the launch method
• Override the start method to set up your program.

All the World’s a Stage

• Top level display container is a stage
• User interface items are contained in a scene
• Only one scene at a time can be displayed on a stage.
• The Application start method takes a stage.
• Set the title
• Set the scene
• Show the stage

SceneGraph and Nodes

• The Scene contains a scene graph, containing all the components of the user interface.
• User interface objects are nodes, derived from Node class.
• Nodes are groups, layouts, controls, shapes, etc.

Layouts are Nodes

• In Swing, you would create a JPanel, configure its LayoutManager, and add components to the panel.
• In JavaFX, a layout is a subclass of Node and contains a collection of other nodes.
• Many Layouts will feel familiar: Border Pane, FlowPane, GridPane, etc.

Event Handling

• Like Swing, JavaFX uses event handlers to respond to user input.
• The EventHandler interface expects a type parameter for which type of event it handles.
• Add the handler object to a node using addEventHandler method.

Hello World

public class Hello extends Application {
    public static void main(String[] args) { launch(args); }
    @Override
    public void start (Stage primaryStage) {
        primaryStage.setTitle("Hello World!");
        Button btn = new Button();
        btn.setText("Say 'Hello World'");
        btn.setOnAction (new EventHandler<ActionEvent>() {
            @Override
            public void handle (ActionEvent event) {
                System.out.println("Hello World!");
            }
        });
        StackPane root = new StackPane();
        root.getChildren().add(btn);
        primaryStage.setScene (new Scene (root, 300, 250));
        primaryStage.show();
    }
}

Lambda Syntax

• Anonymous inner class in previous example could be replaced with lambda syntax.

  btn.setOnAction (event -> {
      System.out.println("Hello World!");
  });

• Single statement body could leave out curly braces.

  btn.setOnAction (event -> System.out.println("Hello World!"));

Drawing on Canvas

public class CanvasDemo extends Application {
    public static void main(String[] args) { launch(args); }
    @Override
    public void start (Stage stage) {
        stage.setTitle("Canvas Drawing Demo");
        Canvas canvas = new Canvas (300, 200);
        GraphicsContext gc = canvas.getGraphicsContext2D();
        gc.setFill (Color.GOLD);
        gc.fillPolygon(new double[]{150, 300, 450}, new double[]{150, 0, 150}, 3);
        gc.fillPolygon(new double[]{0, 150, 300}, new double[]{300, 150, 300}, 3);
        gc.fillPolygon(new double[]{300, 450, 600}, new double[]{300, 150, 300}, 3);
        stage.setScene (new Scene (new StackPane (canvas)));
        stage.show();
    }
}

Mouse Events

public class MouseEventDemo extends Application {
    public static void main(String[] args) { launch(args); }
    @Override
    public void start (Stage stage) {
        stage.setTitle("Mouse Object Demo");
        Canvas canvas = new Canvas(700, 500);
        canvas.addEventHandler(MouseEvent.MOUSE_PRESSED, event -> {
            System.out.println("pressed"+ event.getX() +""+ event.getY());
        });
        canvas.setOnMouseMoved (event -> {
            System.out.println("moved"+ event.getX() +""+ event.getY());
        });
        stage.setScene (new Scene (new StackPane (canvas)));
        stage.show();
    }
}

Animation Timer

• Can use as main program loop in JavaFX program.
• Implement handle method
• Argument is current time in nanoseconds
• Time between calls to handle may vary depending on other program events.

Elapsed Time with java.time.Duration

public class TimerDisplay extends Application {
    public static void main ( String [ ] args ) { launch ( args ); }
    @Override
    public void start ( Stage primaryStage ) {
        primaryStage.setTitle ("Time Display Demo");
        Label text = new Label ( );
        primaryStage.setScene ( new Scene ( text , 200 , 100 ) );
        primaryStage.show ( );
        AnimationTimer a = new AnimationTimer ( ) {
            private long startTime = -1;
            @Override
            public void handle ( long now ) {
                if ( startTime < 0 ) { startTime = now; }
                Duration elapsed = Duration.ofNanos ( now - startTime );
                long minutes = elapsed.toMinutes ( );
                long seconds = elapsed.getSeconds ( ) - minutes * 60;
                String str = String.format ("elapsed time %2d:%02d", minutes , seconds );
                text.setText ( str );
            }
        };
        a.start ( );
    }
}

Encapsulating Mouse State 1/2

public class MouseStateInfo {
    private double x;
    private double y;
    public EventHandler<MouseEvent> getMouseHandler ( ) {
        return event -> {
            x = event.getX ( );
            y = event.getY ( );
        };
    }
    public double getX ( ) { return x; }
    public double getY ( ) { return y; }
}

Encapsulating Mouse State 2/2

public class MouseStateObjectDemo extends Application {
    public static void main ( String [ ] args ) { launch ( args ); }
    @Override
    public void start ( Stage stage ) {
        stage.setTitle ("Mouse Object Demo");
        Canvas canvas = new Canvas ( 700 , 500 );
        MouseStateInfo info = new MouseStateInfo ( );
        canvas.setOnMouseMoved ( info.getMouseHandler ( ) );
        stage.setScene ( new Scene ( new StackPane ( canvas ) ) );
        stage.show ( );
        // Print out mouse location every second
        AnimationTimer a = new AnimationTimer ( ) {
            private long nextTime = 0;
            @Override
            public void handle ( long now ) {
                if ( now > nextTime ) {
                    System.out.println ("mouse at"+ info.getX ( ) + 
                                        ""+ info.getY ( ) );
                    nextTime = now + Duration.ofSeconds ( 1 ) . toNanos ( );
                }
            }
        };
        a.start ( );
    }
}