JavaCC (https://javacc.dev.java.net/) is a Java-based top-down parser generator. It takes a .jj file as input and produces a collection of Java sources. DrJava uses it to produce Java parsers in both DynamicJava and Language Levels.

Newer versions of JavaCC added support for generics and cleaned up a lot of generated code that was producing compiler warnings. Thus, version 4.1 or later is preferred for development in DrJava.