A DESCRIPTION OF THE PROBLEM :
Quote from docs: Note: The ButtonGroup object is a logical grouping -- not a physical grouping. Tocreate a button panel, you should still create a JPanel or similar container-object and add a Border to it to set it off from surrounding components.

s/Tocreate (a button panel)/To create $1/;

  See also bug 4216833 (NOT A DUPE) where the same section was quoted (including this error) but from version 1.2. (likely not a regression)


URL OF FAULTY DOCUMENTATION :
http://java.sun.com/javase/6/docs/api/javax/swing/JRadioButton.html