Synchronize Data Models—Binding and Triggers - JavaFX: Developing Rich Internet Applications - page 71

Figure 4.1 The Two Individual Display States for This Application Depend upon

Where the Mouse Is Located

or exits the image on the display. When the mouse pointer enters the image,
the onMouseEntered handler will be executed setting the currentImage
variable to image1 . When the mouse leaves the image, the onMouseExited
handler will execute setting currentImage to image2 .
3. The actual display is updated by binding the value of currentImage to
ImageView 's image instance variable. In particular, the line of code repre-
sented by image: bind currentImage makes this happen.

Binding with Arithmetic and Logical Expressions
When binding to arithmetic and logical expressions, a bind recalculation takes
place if any component of the expression appearing to the right of the bind key-
word changes. Let's run through an example to demonstrate:

var a = 3;
var b = 4;
var c = a * b;
var d = 7;
var total = bind c + d;
println("total={total}");
d = 10;
println("total={total}");
b = 5;
println("total={total}");

prints out:

total=19
total=22
total=22

The definition of the variable total specifies that its value will be recalculated
whenever c or d change. The second line of output ( total=22 ) is the result of a