Java with Traits — Improving Opportunities for Reuse

The Java language includes features that present significant barriers to reuse; in practice, programmers have no choice but to copy and paste code that is not accessible via inheritance. Traits improve code-sharing in Smalltalk by providing a means to reuse such behavior, and we claim that a similar mechanism for Java would overcome not just the lack of multiple inheritance but Java’s other barriers to reuse as well, including the use of private, final and synchronized qualifiers. In support of our claim we present the initial findings of a case study of Java Swing, a large production-quality library, showing how we isolated pieces of duplicated code that could not be eliminated by conventional means and how traits could be used to eliminate them.