To use PropertyValue, you first need to load GUIKit using Needs["GUIKit`"].
PropertyValue returns the value of the property name.
If the target argument is not present, the target is defaulted to the wrapping widget of the PropertyValue expression.
The target can either be specified as a string name of a widget reference or a component instance such as a JavaObject.
Note that indices in Mathematica and XML widget definitions are 1-based, while Java and direct calls to Java objects using J/Link follow the 0-based Java convention.