Field initializers are called _after_ constructor of superclass, but their values are needed during update of UI delegate (that is called from the constructor of superclass). Hence, moving initialization of borderPainted and contentAreaFilled properties into init() method that is called before updateUI().
Field initializers are called _after_ constructor of superclass, but their
values are needed during update of UI delegate (that is called from
the constructor of superclass). Hence, moving initialization
of borderPainted and contentAreaFilled properties into init() method
that is called before updateUI().

certusoft/swingx,certusoft/swingx