JFlex

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JFlex is an open source grammar language created in 2003.

Source code:

git clone https://github.com/jflex-de/jflex

#377on PLDB

21Years Old

2Repos

JFlex is a lexical analyzer generator (also known as scanner generator) for Java, written in Java.

JFlex website
JFlex is developed on GitHub and has 469 stars
There are at least 2 JFlex repos on GitHub
JFlex first developed in https://github.com/jflex-de/
file extensions for JFlex include flex and jflex
The Google BigQuery Public Dataset GitHub snapshot shows 38 users using JFlex in 39 repos on GitHub
GitHub supports syntax highlighting for JFlex

Example from Linguist:

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright (C) 1998-2015  Gerwin Klein <lsf@jflex.de>                    *
 * All rights reserved.                                                    *
 *                                                                         *
 * License: BSD                                                            *
 *                                                                         *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/* Java 1.2 language lexer specification */

/* Use together with unicode.flex for Unicode preprocesssing */
/* and java12.cup for a Java 1.2 parser                      */

/* Note that this lexer specification is not tuned for speed.
   It is in fact quite slow on integer and floating point literals, 
   because the input is read twice and the methods used to parse
   the numbers are not very fast. 
   For a production quality application (e.g. a Java compiler) 
   this could be optimized */


import java_cup.runtime.*;

%%

%public
%class Scanner
%implements sym

%unicode

%line
%column

%cup
%cupdebug

%{
  StringBuilder string = new StringBuilder();
  
  private Symbol symbol(int type) {
    return new JavaSymbol(type, yyline+1, yycolumn+1);
  }

  private Symbol symbol(int type, Object value) {
    return new JavaSymbol(type, yyline+1, yycolumn+1, value);
  }

  /** 
   * assumes correct representation of a long value for 
   * specified radix in scanner buffer from <code>start</code> 
   * to <code>end</code> 
   */
  private long parseLong(int start, int end, int radix) {
    long result = 0;
    long digit;

    for (int i = start; i < end; i++) {
      digit  = Character.digit(yycharat(i),radix);
      result*= radix;
      result+= digit;
    }

    return result;
  }
%}

/* main character classes */
LineTerminator = \r|\n|\r\n
InputCharacter = [^\r\n]

WhiteSpace = {LineTerminator} | [ \t\f]

/* comments */
Comment = {Tradi

Feature	Supported	Token	Example
Comments	✓		/* A comment */
MultiLine Comments	✓	/* */	/* A comment */
Semantic Indentation	X

JFlex - Grammar language

Language features