EVENT-DRIVEN PROGRAMMING AND ANIMATIONS - Introduction to Java Programming: Comprehensive Version - page 587

The EventHandler<ActionEvent> interface contains the handle(ActionEvent)
method for processing the action event. Your handler class must override this method to
respond to the event. Listing 15.1 gives the code that processes the ActionEvent on the two
buttons. When you click the OK button, the message “OK button clicked” is displayed. When
you click the Cancel button, the message “Cancel button clicked” is displayed, as shown in
Figure 15.2.

L ISTING 15.1

HandleEvent.java
1 import javafx.application.Application;
2 import javafx.geometry.Pos;
3 import javafx.scene.Scene;
4 import javafx.scene.control.Button;
5 import javafx.scene.layout.HBox;
6 import javafx.stage.Stage;
7 import javafx.event.ActionEvent;
8 import javafx.event.EventHandler;
9
10 public class HandleEvent extends Application {
11 @Override // Override the start method in the Application class
12 public void start(Stage primaryStage) {
13 // Create a pane and set its properties
14 HBox pane = new HBox( 10 );
15 pane.setAlignment(Pos.CENTER);
16 Button btOK = new Button( "OK" );
17 Button btCancel = new Button( "Cancel" );
18 OKHandlerClass handler1 = new OKHandlerClass();
19 btOK.setOnAction(handler1);
20 CancelHandlerClass handler2 = new CancelHandlerClass();
21 btCancel.setOnAction(handler2);
22 pane.getChildren().addAll(btOK, btCancel);
23
24 // Create a scene and place it in the stage
25 Scene scene = new Scene(pane);
26 primaryStage.setTitle( "HandleEvent" ); // Set the stage title
27 primaryStage.setScene(scene); // Place the scene in the stage
28 primaryStage.show(); // Display the stage
29 }
30 }
31
32 class OKHandlerClass implements EventHandler<ActionEvent> {
33 @Override
34 public void handle(ActionEvent e) {
35 System.out.println( "OK button clicked" );
36 }
37 }
38
39 class CancelHandlerClass implements EventHandler<ActionEvent> {
40 @Override
41 public void handle(ActionEvent e) {
42 System.out.println( "Cancel button clicked" );
43 }
44 }

create handler
register handler
create handler
register handler

handler class

handle event

handler class

handle event

Two handler classes are defined in lines 32-44. Each handler class implements
EventHandler<ActionEvent> to process ActionEvent . The object handler1 is an
instance of OKHandlerClass (line 18), which is registered with the button btOK (line
19). When the OK button is clicked, the handle(ActionEvent) method (line 34) in