You need ANTLRWorks to generate the parser. Download version 1.4.2 (or ANTLR 3.3)  (NOT 1.5, which doesn't work with the current grammar file). Then in the configuration settings of ANTLRWorks set the output directory to '.' such that it generates files in the same directory as the grammar file. Open Java.g with ANTLRWorks and generate the parser. Due to a bug in ANTLR, you need to fix 1 compile error in the generated parser: set the package. In Eclipse you can use CTRL (or COMMAND) + 1 and use the suggested fix. Because of the bug, that part of the build must be done manually.