  A common approach to improve software quality is to use programming
guidelines to avoid common kinds of errors. In this paper, we consider the
problem of enforcing guidelines for Featherweight Java (FJ). We formalize
guidelines as sets of finite or infinite execution traces and develop a
region-based type and effect system for FJ that can enforce such guidelines. We
build on the work by Erbatur, Hofmann and Z\u{a}linescu, who presented a type
system for verifying the finite event traces of terminating FJ programs. We
refine this type system, separating region typing from FJ typing, and use ideas
of Hofmann and Chen to extend it to capture also infinite traces produced by
non-terminating programs. Our type and effect system can express properties of
both finite and infinite traces and can compute information about the possible
infinite traces of FJ programs. Specifically, the set of infinite traces of a
method is constructed as the greatest fixed point of the operator which
calculates the possible traces of method bodies. Our type inference algorithm
is realized by working with the finitary abstraction of the system based on
B\"uchi automata.
