JAVAFX BASICS - Introduction to Java Programming: Comprehensive Version - page 543

updates itself once a change is made in the source. A target binds with a source using the bind
method as follows:
target.bind(source);
The bind method is defined in the javafx.beans.property.Property interface. A
binding property is an instance of javafx.beans.property.Property . A source object is an
instance of the javafx.beans.value.ObservableValue interface. An ObservableValue
is an entity that wraps a value and allows to observe the value for changes.
JavaFX defines binding properties for primitive types and strings. For a double / float /
long / int / boolean value, its binding property type is DoubleProperty / FloatProperty /
LongProperty / IntegerProperty / BooleanProperty . For a string, its binding property
type is StringProperty . These properties are also subtypes of ObservableValue . So they
can also be used as source objects for binding properties.
By convention, each binding property (e.g., centerX ) in a JavaFX class (e.g., Circle ) has a
getter (e.g., getCenterX() ) and setter (e.g., setCenterX(double) ) method for returning and
setting the property's value. It also has a getter method for returning the property itself. The naming
convention for this method is the property name followed by the word Property . For example,
the property getter method for centerX is centerXProperty() . We call the getCenterX()
method as the value getter method , the setCenterX(double) method as the value setter method ,
and centerXProperty() as the property getter method . Note that getCenterX() returns
a double value and centerXProperty() returns an object of the DoubleProperty type.
Figure 14.7a shows the convention for defining a binding property in a class and Figure 14.7b
shows a concrete example in which centerX is a binding property of the type DoubleProperty .

the Property interface

the ObservableValue
interface

common binding properties

common ObservableValue
objects

value getter method
value setter method
property getter method

public class SomeClassName { public class Circle {

private PropertyType x; private DoubleProperty centerX;

/** Value getter method */
public propertyValueType getX() { ... }

/** Value getter method */
public double getCenterX() { ... }

/** Value setter method */
public void setX(propertyValueType value) { ... }

/** Value setter method */
public void setCenterX( double value) { ... }

/** Property getter method */
public PropertyType
xProperty() { ... }
}

/** Property getter method */
public DoubleProperty centerXProperty() { ... }

}

(b) centerX is binding property

(a) x is a binding property

F IGURE 14.7

A binding property has a value getter method, setter method, and property getter method.

The program in Listing 14.5 is the same as in Listing 14.4 except that it binds circle 's
centerX and centerY properties to half of pane 's width and height (lines 16-17). Note that
circle.centerXProperty() returns centerX and pane.widthProperty() returns
width . Both centerX and width are binding properties of the DoubleProperty type. The
numeric binding property classes such as DoubleProperty and IntegerProperty con-
tain the add , subtract , multiply , and divide methods for adding, subtracting, multiply-
ing, and dividing a value in a binding property and returning a new observable property. So,
pane.widthProperty().divide(2) returns a new observable property that represents
half of the pane 's width. The statement
circle.centerXProperty().bind(pane.widthProperty().divide( 2 ));
is same as

centerX.bind(width.divide( 2 ));