Modern Java languages introduce several new features that offer significant improvements over older Java technology. In this article we consider the new enum construct, which provides language support for enumerated types. Prior to recent Java languages, programmers needed to employ various patterns (e.g., the weak enum pattern) to compensate for the absence of enumerated types in Java. Unfortunately, these compensation patterns lack several highly-desirable properties of the enum construct, most notably, type safety. We present a novel fully-automated approach for transforming legacy Java code to use the new enumeration construct. This semantics-preserving approach increases type safety, produces code that is easier to comprehend, removes unnecessary complexity, and eliminates brittleness problems due to separate compilation. At the core of the proposed approach is an interprocedural type inferencing algorithm which tracks the flow of enumerated values. The algorithm was implemented as an open source, publicly available Eclipse plug-in and evaluated experimentally on 17 large Java benchmarks. Our results indicate that analysis cost is practical and the algorithm can successfully refactor a substantial number of fields to enumerated types. This work is a significant step towards providing automated tool support for migrating legacy Java software to modern Java technologies.