2 Working with Convenience Methods

Using Convenience Methods

Many of the convenience methods are defined in the Node class and are available to all of its subclasses. Other classes also contain convenience methods. Table 2-1 describes the events that convenience methods can be used to handle and identifies the classes in which the convenience methods are defined.

Convenience methods for registering event handlers have the following format:

setOnEvent-type(EventHandler<? super event-class> value)

Event-type is the type of event that the handler processes, for example, setOnKeyTyped for KEY_TYPED events or setOnMouseClicked for MOUSE_CLICKED events. event-class is the class that defines the event type, for example, KeyEvent for events related to keyboard input or MouseEvent for events related to mouse input. The string <? super event-class> indicates that the method accepts an event handler for event-class or an event handler for one of its super classes as the argument. For example, an event handler for InputEvent could be used when the event is either a keyboard event or a mouse event.

The following statement shows the definition for the method that registers an event handler to handle the events that are generated when a key is typed, that is, when a key is pressed and released:

setOnKeyTyped(EventHandler<? super KeyEvent> value)

You can create and register your event handler in a single step by defining the handler as an anonymous class in the call to the convenience method. The event handler must implement the handle() method to provide the code needed to process the event.

A example of the use of a convenience method is shown in the code that is generated when you use the NetBeans IDE to create a JavaFX application. If you select the Create Application Class option when you create your JavaFX application, the main class that is created contains a "Hello World" application. The generated code is shown in Example 2-1.

package yourapplication;
 
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.stage.Stage;
 
public class YourApplication extends Application {
 
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        Application.launch(args);
    }
    
    @Override
    public void start(Stage primaryStage) {
        primaryStage.setTitle("Hello World");
        Group root = new Group();
        Scene scene = new Scene(root, 300, 250);
        Button btn = new Button();
        btn.setLayoutX(100);
        btn.setLayoutY(80);
        btn.setText("Hello World");
        btn.setOnAction(new EventHandler<ActionEvent>() {
 
            public void handle(ActionEvent event) {
                System.out.println("Hello World");
            }
        });
        root.getChildren().add(btn);
        primaryStage.setScene(scene);
        primaryStage.show();
    }
}

The "Hello World" code creates a window with a single button. The setOnAction() method is used to register an event handler that handles the action events that are dispatched when the button is clicked. The handle() method in the event handler handles the event by printing the string "Hello World" to the console.

final Circle circle = new Circle(radius, Color.RED); 

circle.setOnMouseEntered(new EventHandler<MouseEvent>() {
    public void handle(MouseEvent me) {
        System.out.println("Mouse entered"); 
    }
});

circle.setOnMouseExited(new EventHandler<MouseEvent>() {
    public void handle(MouseEvent me) {
        System.out.println("Mouse exited");
    }
});

circle.setOnMousePressed(new EventHandler<MouseEvent>() {
    public void handle(MouseEvent me) {
        System.out.println("Mouse pressed");
    }
});

final TextField textBox = new TextField();
textBox.setPromptText("Write here");

textBox.setOnKeyPressed(new EventHandler<KeyEvent>() {
    public void handle(KeyEvent ke) {
        System.out.println("Key Pressed: " + ke.getText());
    }
});

textBox.setOnKeyReleased(new EventHandler<KeyEvent>() {
    public void handle(KeyEvent ke) {
        System.out.println("Key Released: " + ke.getText());
    }
});

Additional Resources

For information on the available convenience methods, see the JavaFX API documentation.