JAVAFX BASICS - Introduction to Java Programming: Comprehensive Version - page 544

Since centerX is bound to width.divide(2) , when pane 's width is changed, centerX
automatically updates itself to match pane 's width / 2.
Listing 14.6 gives another example that demonstrates bindings.

L ISTING 14.6

BindingDemo.java
1 import javafx.beans.property.DoubleProperty;
2 import javafx.beans.property.SimpleDoubleProperty;
3
4 public class BindingDemo {
5 public static void main(String[] args) {
6 DoubleProperty d1 = new SimpleDoubleProperty( 1 );
7 DoubleProperty d2 = new SimpleDoubleProperty( 2 );
8 d1.bind(d2);
9 System.out.println( " d1 is " + d1.getValue()
10 + " and d2 is " + d2.getValue());
11 d2.setValue( 70.2 );
12 System.out.println( " d1 is " + d1.getValue()
13 + " and d2 is " + d2.getValue());
14 }
15 }

create a DoubleProperty
create a DoubleProperty
bind property

set a new source value

d1 is 2.0 and d2 is 2.0
d1 is 70.2 and d2 is 70.2

The program creates an instance of DoubleProperty using
SimpleDoubleProperty(1) (line 6). Note that DoubleProperty , FloatProperty ,
LongProperty , IntegerProperty , and BooleanProperty are abstract classes. Their
concrete subclasses SimpleDoubleProperty , SimpleFloatProperty , SimpleLong-
Property , SimpleIntegerProperty , and SimpleBooleanProperty are used to cre-
ate instances of these properties. These classes are very much like wrapper classes Double ,
Float , Long , Integer , and Boolean with additional features for binding to a source object.
The program binds d1 with d2 (line 8). Now the values in d1 and d2 are the same. After
setting d2 to 70.2 (line 11), d1 also becomes 70.2 (line 13).
The binding demonstrated in this example is known as unidirectional binding . Occasion-
ally, it is useful to synchronize two properties so that a change in one property is reflected in
another object, and vice versa. This is called a bidirectional binding . If the target and source
are both binding properties and observable properties, they can be bound bidirectionally using
the bindBidirectional method.
14.8 What is a binding property? What interface defines a binding property? What inter-
face defines a source object? What are the binding object types for int , long ,
float , double , and boolean ? Are Integer and Double binding properties? Can
Integer and Double be used as source objects in a binding?
14.9 Following the JavaFX binding property naming convention, for a binding property
named age of the IntegerProperty type, what is its value getter method, value
setter method, and property getter method?
14.10 Can you create an object of IntegerProperty using new IntegerProperty(3) ?
If not, what is the correct way to create it? What will the output if line 8 is replaced
by d1.bind(d2.multiply(2)) in Listing 14.6? What will the output if line 8 is
replaced by d1.bind(d2.add(2)) in Listing 14.6?

unidirectional binding

bidirectional binding

✓ ✓

Check

Point

14.11

What is a unidirectional binding and what is bidirectional binding? Are all binding
properties capable of bidirectional binding? Write a statement to bind property d1
with property d2 bidirectionally.