A Nano-Pattern Language for Java

Patterns, micro-patterns, and nano-patterns have many applications: program comprehension, code transformations, documentation aids, improving code robustness, etc. This work revisits the notion of nano-patterns—originally an obiter dictum of the work on micro-patterns. Nano-patterns here are taken as more general than their previous definition in the literature: predicates on short code snippets that represent some common and elementary programming missions such as “for each m ∈ M do…”, or, “use x (but if x is null, y is a substitute)”, which represent small and recurring programming idioms. With this generalization, we offer a taxonomized languageof nanos nano-patterns for Java. We also describe the process of pattern harvesting we used and the underlying rationale, including our proposed prevalence threshold criterion, which, by capitalizing on Hirsch's famous h-index, makes a robust yard-stick of the pattern's significance. An empirical survey of 78 Open Source Java projects indicates that the nano-patterns of our proposed language described here have a substantial prevalence in the code. About a third of the commands (executable statements) and half of the methods are instances of nano-patterns in the proposed language. Also, the language's prevalence is typically higher than that of languages harvested in a project specific, automated machine learning process. Nano-patterns are implementation/language level details for most high level software engineering purposes. One contribution made by the present paper is in identifying the clutter made by the snippets, appreciating its presence, and imposing order on it. The language, the nano-patterns in it, and the contributed automatic tool for tracing nano-patterns in code may help to deal systematically with this low level, yet significant, portion of code.