JavaFX is a GUI framework in Java used for building rich desktop applications. It provides tools for 2D/3D graphics, media, UI controls, CSS styling, and event handling mechanisms.

The three main components are:
• Stage – The top-level window.
• Scene – Holds all UI components (nodes).
• Nodes – The individual visual elements (like Button, Text, or ImageView).

Every JavaFX program extends the Application class and follows this sequence:
1️⃣ init() – initializes variables/resources.
2️⃣ start(Stage primaryStage) – builds and shows the UI.
3️⃣ stop() – cleans up resources before exit.

An event represents an action or interaction in the UI, such as a mouse click, key press, or window resize. JavaFX uses event objects to describe and handle these interactions.

Common event types include:
• ActionEvent – triggered by buttons or menu items.
• MouseEvent – when the mouse is clicked, moved, or dragged.
• KeyEvent – keyboard input events.
• WindowEvent – window actions like close or minimize.

Event Source is the node that triggers the event (like a Button).
Event Target is the node that receives and handles the event.

class MyButtonHandler implements EventHandler<ActionEvent> {
    public void handle(ActionEvent e) {
        System.out.println("Button clicked!");
    }
}

Button btn = new Button("Click Me");
btn.setOnAction(new MyButtonHandler());

This approach separates logic from the UI code — useful for clarity and reusability.

class CircleClickHandler implements EventHandler<MouseEvent> {
    public void handle(MouseEvent e) {
        System.out.println("Mouse clicked at: " + e.getX() + ", " + e.getY());
    }
}

Circle circle = new Circle(50, Color.CORNFLOWERBLUE);
circle.setOnMouseClicked(new CircleClickHandler());

Pane pane = new Pane();
pane.setOnMouseClicked(new EventHandler<MouseEvent>() {
    public void handle(MouseEvent e) {
        Circle c = new Circle(e.getX(), e.getY(), 10, Color.DODGERBLUE);
        pane.getChildren().add(c);
    }
});

📘 This demonstrates dynamic UI creation using mouse coordinates.

Rectangle box = new Rectangle(100, 50, Color.LIGHTGRAY);
box.setOnMouseEntered(e -> box.setFill(Color.LIGHTGREEN));
box.setOnMouseExited(e -> box.setFill(Color.LIGHTGRAY));

class KeyHandler implements EventHandler<KeyEvent> {
    public void handle(KeyEvent e) {
        System.out.println("Key Pressed: " + e.getCode());
    }
}

scene.setOnKeyPressed(new KeyHandler());

Scene Builder is a drag-and-drop tool for designing JavaFX user interfaces visually.
• It automatically generates FXML files.
• It allows quick design without writing code.
• Helps separate UI layout from application logic.
• Increases productivity and reduces syntax errors.

Text msg = new Text(100, 120, "Welcome to JavaFX!");
msg.setFont(Font.font("Arial", 20));
msg.setFill(Color.DARKBLUE);

This displays styled text on the scene at position (100,120).

Image img = new Image("file:photo.png");
ImageView view = new ImageView(img);
view.setFitWidth(200);
view.setPreserveRatio(true);

💡 Tip: Always use setPreserveRatio(true) to maintain aspect ratio.

Stage is the main application window, while Scene is the content area that holds and displays all UI components (nodes) inside that stage.