JavaCC
Java Compiler Compiler (JavaCC) is the most popular parser generator for use with Java [tm] applications. A parser generator is a tool that reads a grammar specification and converts it to a Java program that can recognize matches to the grammar. In addition to the parser generator itself, JavaCC provides other standard capabilities related to parser generation such as tree building (via a tool called JJTree included with JavaCC), actions, debugging, etc.
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License
BSD License