A format string checker for Java

Abstract

Java supports format strings, but their use is error prone because: Java's type system does not find any but the most trivial mistakes, Java's format methods fail silently, and format methods are often executed infrequently.This paper presents the Format String Checker that is based on the format string type system presented in [3]. The Format String Checker guarantees that calls to Java's Formatter API will not throw exceptions.We evaluate the Format String Checker on 6 large and well-maintained open-source projects. Format string bugs are common in practice (we found 104 bugs), and the annotation burden on the user of our type system is low (on average, for every bug found, only 1.0 annotations need to be written).