Even in these days of sophisticated graphical user interfaces, many programs have a wide variety of command line options that help specify their behavior. It is also the case that command line only programs continue to enjoy wide use. It is also the case the command line arguments can become quite complicated, e.g.: -Djava.util.logging.config.file=All.finest -1 --list --this=that Some languages have built-in parsers for command line options; perl and bash are two obvious examples of this. Java has no such parser built in. The JCLO package provides the capability to parse several different command line option formats, and uses Java's reflecion mechanizm to both drive the parsing and assign the values provided by command line options to the variable in a specified class.