EVENT-DRIVEN PROGRAMMING AND ANIMATIONS - Introduction to Java Programming: Comprehensive Version - page 595

public void start(Stage primaryStage) {
// Omitted

public void start(Stage primaryStage) {
// Omitted

btEnlarge.setOnAction(
new EnlargeHandler());

btEnla rge.setOnAction(
ne w class En largeHandlner
implements EventHandler<ActionEvent>() {
public void handle(ActionEvent e) {
circlePane.enlarge();
}
});
}

}

class EnlargeHandler
implements EventHandler<ActionEvent> {
public void handle(ActionEvent e) {
circlePane.enlarge();
}
}

(a) Inner class EnlargeListener (b) Anonymous inner class

The syntax for an anonymous inner class is shown below

new SuperClassName/InterfaceName() {
// Implement or override methods in superclass or interface

// Other methods if necessary

}

Since an anonymous inner class is a special kind of inner class, it is treated like an inner class
with the following features:

An anonymous inner class must always extend a superclass or implement an inter-
face, but it cannot have an explicit extends or implements clause.

■

An anonymous inner class must implement all the abstract methods in the superclass
or in the interface.

■

An anonymous inner class always uses the no-arg constructor from its superclass to
create an instance. If an anonymous inner class implements an interface, the con-
structor is Object() .

■

An anonymous inner class is compiled into a class named OuterClassName$ n .
class . For example, if the outer class Test has two anonymous inner classes, they
are compiled into Test$1.class and Test$2.class .

■

Listing 15.4 gives an example that handles the events from four buttons, as shown in
Figure 15.8.

F IGURE 15.8

The program handles the events from four buttons.

L ISTING 15.4

AnonymousHandlerDemo.java
1 import javafx.application.Application;
2 import javafx.event.ActionEvent;
3 import javafx.event.EventHandler;
4 import javafx.geometry.Pos;
5 import javafx.scene.Scene;

VideoNote

Anonymous handler