JavaCC == Java Compiler Compiler
A funny way of saying, "A java program that compiles a syntax definition into a language compiler (i.e. language parser)."
You feed JavaCC text files that describe the syntax of any language, and it will produce the source code of a java program that can parse your language and make sure the source is valid.
Language syntax definitions are abundant for JavaCC, including definitions for Java 1.0.2 and Java 1.1. (Others include C and C++.)
You can essentially create your own language, and use JavaCC to create a parser for it.
More info: http://www.suntest.com/javacc/