EVENT-DRIVEN PROGRAMMING AND ANIMATIONS - Introduction to Java Programming: Comprehensive Version - page 597

The anonymous inner classes in this example are compiled into
AnonymousHandlerDemo$1.class , AnonymousHandlerDemo$2.class ,
AnonymousHandlerDemo$3.class , and AnonymousHandlerDemo$4.class .

15.9

✓ ✓

If class A is an inner class in class B , what is the .class file for A ? If class B contains
two anonymous inner classes, what are the .class file names for these two classes?

Check

Point

15.10

What is wrong in the following code?

public class Test extends Application {
public void start(Stage stage) {
Button btOK = new Button( "OK" );
}

public class Test extends Application {
public void start(Stage stage) {
Button btOK = new Button( "OK" );

btOK.setOnAction(
new EventHandler<ActionEvent> {
public void handle
(ActionEvent e) {
System.out.println
(e.getSource());
}
} // Something missing here
}
}

private class Handler implements
EventHandler<ActionEvent> {
public void handle(Action e) {
System.out.println(e.getSource());
}
}
}

(a)

(b)

15.6 Simplifying Event Handling Using Lambda
Expressions
Lambda expressions can be used to greatly simplify coding for event handling.

Key
Point

Lambda expression is a new feature in Java 8. Lambda expressions can be viewed as an
anonymous class with a concise syntax. For example, the following code in (a) can be greatly
simplified using a lambda expression in (b) in three lines.

lambda expression

btEnlarge.setOnAction(e -> {
// Code for processing event e
});

btEnlarge.setOnAction(
new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent e) {
// Code for processing event e

}
}
});

(a) Anonymous inner class event handler (b) Lambda expression event handler

The basic syntax for a lambda expression is either

(type1 param1, type2 param2, ...) -> expression

or

(type1 param1, type2 param2, ...) -> { statements; }