Boolean operators

A binding path expression can be prefixed with a boolean operator, which causes the expression to evaluate to a boolean value.

Operator	Description
!	inverts the boolean value; converts 0 or null to true
!!	inverts the boolean value twice; converts 0 or null to false

In the following example, the controls are disabled or hidden when the bound list is empty:

<!-- disabled=true when size=0 -->
<MyAddressControl disabled="${!user::addresses.size}"/>

<!-- visible=false when size=0 -->
<MyAddressControl visible="${!!user::addresses.size}"/>

Applicability

A boolean operator is applicable to any expression type, not just boolean expressions. However, restrictions apply for some binding modes.

Binding mode	Applicable
fx:once	yes, all expression types
fx:bind	yes, all expression types
fx:bindBidirectional	only if the binding source implements WritableValue<Boolean> (e.g. DoubleProperty)
fx:content	no
fx:bindContent	no
fx:bindContentBidirectional	no