Java Reference
In-Depth Information
ymous inner class and creates one object of that class. A reference to that object is then
passed to
addListener
. After the
new
keyword, the syntax
ChangeListener<Number>()
(line 69) begins the declaration of an anonymous inner class that implements interface
ChangeListener<Number>
. This is similar to beginning a class declaration with
public class
MyHandler
implements
ChangeListener<Number>
The opening left brace at 70 and the closing right brace at line 79 delimit the body of
the anonymous inner class. Lines 71-78 declare the
ChangeListener<Number>
's
changed
method, which receives a reference to the
ObservableValue
that changed, a
Number
con-
taining the
Slider
's old value before the event occurred and a
Number
containing the
Slider
's new value. When the user moves the
Slider
's thumb, lines 75-76 store the new
tip percentage and line 77 updates the
tipPercentageLabel
.
An anonymous inner class can access its top-level class's instance variables,
static
variables and methods—in this case, the anonymous inner class uses instance variables
tipPercentage
and
tipPercentageLabel
, and
static
variable
percent
.
However, an
anonymous inner class has limited access to the local variables of the method in which it's
declared—it can access only the
final
local variables declared in the enclosing method's
body. (As of Java SE 8, an anonymous inner class may also access a class's effectively
final
local variables—see Section 17.3.1 for more information.)
Java SE 8: Using a Lambda to Implement the
ChangeListener
Recall from Section 10.10 that in Java SE 8 an interface containing one method is a func-
tional interface and recall from Chapter 17 that such interfaces may be implemented with
lambdas. Section 17.9 showed how to implement an event-handling functional interface
using a lambda. The event handler in Fig. 25.21 can be implemented with a lambda as
follows:
tipPercentageSlider.valueProperty().addListener(
(ov, oldValue, newValue) ->
{
tipPercentage =
BigDecimal.valueOf(newValue.intValue() /
100.0
);
tipPercentageLabel.setText(percent.format(tipPercentage));
});
JavaFX is a robust GUI, graphics and multimedia technology. In the online Chapters 26
and 27, you'll:
•
Learn additional JavaFX layouts and controls.
•
Handle other event types (such as
MouseEvent
s).
•
Apply transformations (such as moving, rotating, scaling and skewing) and effects
(such as drop shadows, blurs, reflection and lighting) to a scene graph's nodes.
•
Use CSS to specify the look-and-feel of controls.
•
Use JavaFX properties and data binding to enable automatic updating of controls
as corresponding data changes.
•
Use JavaFX graphics capabilities.
