JavaCC简介

JavaCC是一个java下的词法和语法分析器，它和传统的LEX+YACC组合不同的是，是属于自顶向下的语法分析器，用它来构建java方面的语法分析非常容易。
自顶向下分析也称为面向目标的分析方法，简单说来，就是从文法的开始符号出发企图推到出和输入单词串完全相匹配的句子，若输入串是给定文法的句子，则必然能推导出来，否则报错。采用自顶向下的分析方法允许更通用的语法（但是包含左递归的语法除外）。自顶向下的语法分析器还有其他的一些优点，比如：易于调试，可以分析语法中的任何非终结符，可以在语法分析的过程中在语法分析树中上下传值等。


JavaCC 的下载地址是：https://javacc.java.net/
上面已经有很多入门的例子


以下是一个简单例子
/* Copyright (c) 2006, Sun Microsystems, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *     * Redistributions of source code must retain the above copyright notice,
 *       this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the Sun Microsystems, Inc. nor the names of its
 *       contributors may be used to endorse or promote products derived from
 *       this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */




PARSER_BEGIN(Eg1)


/** An Arithmetic Grammar. */
public class Eg1 {


  /** Main entry point. */
  public static void main(String args[]) {
    System.out.println("Reading from standard input...");
    Eg1 t = new Eg1(System.in);
    try {
      SimpleNode n = t.Start();
      n.dump("");
      System.out.println("Thank you.");
    } catch (Exception e) {
      System.out.println("Oops.");
      System.out.println(e.getMessage());
      e.printStackTrace();
    }
  }
}


PARSER_END(Eg1)




SKIP :
{
  " "
| "\t"
| "\n"
| "\r"
| <"//" (~["\n","\r"])* ("\n"|"\r"|"\r\n")>
| <"/*" (~["*"])* "*" (~["/"] (~["*"])* "*")* "/">
}


TOKEN : /* LITERALS */
{
  < INTEGER_LITERAL:
        <DECIMAL_LITERAL> (["l","L"])?
      | <HEX_LITERAL> (["l","L"])?
      | <OCTAL_LITERAL> (["l","L"])?
  >
|
  < #DECIMAL_LITERAL: ["1"-"9"] (["0"-"9"])* >
|
  < #HEX_LITERAL: "0" ["x","X"] (["0"-"9","a"-"f","A"-"F"])+ >
|
  < #OCTAL_LITERAL: "0" (["0"-"7"])* >
}


TOKEN : /* IDENTIFIERS */
{
  < IDENTIFIER: <LETTER> (<LETTER>|<DIGIT>)* >
|
  < #LETTER: ["_","a"-"z","A"-"Z"] >
|
  < #DIGIT: ["0"-"9"] >
}


/** Main production. */
SimpleNode Start() : {}
{
  Expression() ";"
  { return jjtThis; }
}


/** An Expression. */
void Expression() : {}
{
  AdditiveExpression()
}


/** An Additive Expression. */
void AdditiveExpression() : {}
{
  MultiplicativeExpression() ( ( "+" | "-" ) MultiplicativeExpression() )*
}


/** A Multiplicative Expression. */
void MultiplicativeExpression() : {}
{
  UnaryExpression() ( ( "*" | "/" | "%" ) UnaryExpression() )*
}


/** A Unary Expression. */
void UnaryExpression() : {}
{
  "(" Expression() ")" | Identifier() | Integer()
}


/** An Identifier. */
void Identifier() : {}
{
  <IDENTIFIER>
}


/** An Integer. */
void Integer() : {}
{
  <INTEGER_LITERAL>
}