Getting Started with JavaFX - JavaFX 1.2 Application Development - page 22

Instance level
A variable that is defined at the top-level of a class is referred to as an instance variable.
An instance level is visible within the class by the class members and can be accessed by
creating an instance of the class.
Local level
The least visible scope are local variables. They are declared within code blocks such as
functions. They are visible only to members within the block.
See also
F Creating and using JavaFX classes
F Creating and using JavaFX functions
Using binding and triggers to update
variables
Languages, such as JavaFX, which target a visual domain have to be event-based in order to
handle the non-linearity of GUI interactions. Traditionally, in a visual programming paradigm,
events are generated by components when their internal states are updated. This can require
an elaborate notification-handler syntax to properly express the relationship between event
broadcasters and handlers.
This section explores the easy and intuitive declarative syntax of JavaFX's event-based
programming. It looks at how variable values can remain synchronized using a mechanism
called binding.
Getting ready
This section discusses concepts that require familiarity with variable bindings as found in
other scripting languages. Binding usually refers to the ability to automatically react and
handle events caused by resources (or other events) to which handlers are bound.
How to do it...
JavaFX facilitates variable binding using the bind keyword. Let us look at a simple example
that shows the ease with which you can bind variables. Note that you can find listings for
binding examples at ch01/source-code/src/binding/ .
var step = 100;
def locX = bind step;
println ("locX = {locX}");