See the JavaCC documentation for details. Also see the mini-tutorial on the JavaCC site for tips on writing lexer specifications from which JavaCC can generate. At the end of the tutorial, we will parse a SQL file and extract table specifications ( please note that this is for an illustrative purpose; complete. In this first edition of the new Cool Tools column, Oliver Enseling discusses JavaCC — the Java Compiler Compiler. JavaCC facilitates.

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A string ‘image’ represents the character sequence associated with the token. You still need to read the online documentation to do anything really useful with the tool though.

The Token objects are simply added to an ArrayList and the List is returned. When things get complex, however, having a parser generator at your disposal is a life saver. One way to do this is to use a very large integer value such as the largest possible integer as follows: For the SQL test file, you will get the output as: You will see java code here, because the java code is copied to the java source file for the parser literally.

The generated parser will still work using the default lookahead algorithm – except that it may not do what you expect of it. In other words, javacc creates pure java source files that can run without any external dependencies. Download and install a plug-in Google for easy-javacc I named the parser rule for the demo project parseFile in the section above.


The default values for each of these entities is defined below:. For sophisticated, or bizarre, parsing, sometimes semantic lookahead is needed.

Anybody has some links to javacc tutorials? – Stack Overflow

It contains a String[] where the String at the index of kind, contains a String representation of the Token type. Using JavaCC In practice, the scanning and parsing phases of a compiler are handled by code that jqvacc generated by a parser generator.

Sometimes no number of lookahead tokens is sufficient for the parser. Theodore Norvell 7, 4 16 Jaavcc ab used this in the grammar file, when I stored tokens in the ArrayList: The problem here is that the default LL 1 algorithm will choose the [ “c” ] every time it sees a “c” and therefore “abc” will never be matched.

Getting started in JavaCC

Now the grammar says the next character must be yet another ‘c’. Once you get a good start with creating a simple parser, sure you will find it as a better alternative in many hectic situations. DemoParserConstants is a utility class that can be used to make sense of these numbers. I’m about halfway through the Book now: After successful compilation, you are ready to test a sample file. Here again, there is only one choice for the next input character – it must be ‘b’.

In this example, we are checking the file structure only. So we retrace our steps back to step 3 and make another choice and try that. We have now backtracked and made the other choice we could have made at Step 3 – namely, ignore the [ There are also ways to make “private” tokens, and write complex regular expressions.

An Introduction to JavaCC

We initialize the parser with an InputStream or a Reader, so we can easily parse all sorts of sources. We will add more items to the file in the coming steps.


I will discuss the generated classes in the next section, this section is focused solely on the grammar file. The demo tutoroal will be filled by JavaCC with the parser generated from the grammar file javacc. You can place a bound on the number of tokens to consume during syntactic lookahead as follows: If you desire so, you can add a main method or other custom methods as well.

These grammar files are named with the extension.

Create a folder in the root of the workspace named demo. Similarly, InterfaceDeclaration can start with any number of “abstract”s and “public”s.

Using JavaCC

In this case, the generated parser has to somehow determine which of exp1, exp2, etc. For this example, we are not considering the fields in the Create Table statement.

Sub class of Exception. If you forget to do this, the java compiler will complain that the declared package does not match the expected package. Refresh the root of the project so that eclipse sees the files. Erik Lievaart Recently, I wanted to write my own parser turorial a hobby project.

It starts you off making a simple adder, then calculator. In this case, we made the bad choice in Step 3.