8.1.6 Class Body and Member Declarations
A class body may contain declarations of members of the class, that is, fields (�8.3), classes (�8.5), interfaces (�8.5) and methods (�8.4). A class body may also contain instance initializers (�8.6), static initializers (�8.7), and declarations of constructors (�8.8) for the class.
ClassBody:
{ ClassBodyDeclarationsopt }
ClassBodyDeclarations is "optional".