op4j is a developer happiness tool. It is a Java library aimed at improving quality, semantics, cleanness and readability of Java code, especially auxiliary code like data conversion, structure iteration, filtering, mapping, etc.

op4j is a powerful implementation of the Fluent Interface style of code defined by Martin Fowler. It allows you to create chained expressions which apply both predefined or user-defined functions to your objects in a fluid and readable way. This improves the way your code looks and greatly reduces the complexity of executing auxiliary low-level tasks in the highly bureaucratic, statically and strongly typed language that Java is.