JavaCC (Java Compiler Compiler) is an open-source parser generator and lexical analyzer generator written in the Java programming language. JavaCC is similar to yacc in that it generates a parser from a formal grammar written in EBNF notation. Unlike yacc, however, JavaCC generates top-down parsers. JavaCC can resolve choices based on the next k input tokens, and so can handle LL(k) grammars automatically; by use of "lookahead specifications", it can also resolve choices requiring unbounded look ahead. JavaCC also generates lexical analyzers in a fashion similar to lex. The tree builder that accompanies it, JJTree, constructs its trees from the bottom up.