...when an object of the
anonymous class is instantiated,
copies of the final local variables
and method parameters referred to by
the object's methods are stored as
instance variables in the object. The
methods in the object of the anonymous
class really access those hidden
instance variables.
Thus, the local
variables and method parameters
accessed by the methods of the local
class must be declared final to
prevent their values from changing
after the object is instantiated.
From here.
