刚开始接触 JavaCC。但是我有一个奇怪的行为。我想验证输入 int 形式的标记(字母和数字),它们与符号(+、-、/)连接并且可以包含括号。 我希望这是可以理解的:)
在 main 方法中是一个字符串,应该会产生错误,因为它有一个左括号和两个右括号,但我没有得到解析异常 --> 为什么?
有人知道为什么我没有得到异常吗?
我在最初的尝试中一直在左递归和选择冲突方面苦苦挣扎,但设法克服了它们。也许我在那里介绍了问题?!
哦 - 也许我的解决方案不是很好 - 忽略这个事实......或者更好的是,提供一些建议;-)
文件:代码解析器.jj
options {
STATIC=false;
}
PARSER_BEGIN(CodeParser)
package com.testing;
import java.io.StringReader;
import java.io.Reader;
public class CodeParser {
public CodeParser(String s)
{
this((Reader)(new StringReader(s)));
}
public static void main(String args[])
{
try
{
/** String has one open, but two closing parenthesis --> should produce parse error */
String s = "A+BC+-(2XXL+A/-B))";
CodeParser parser = new CodeParser(s);
parser.expression();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
PARSER_END(CodeParser)
TOKEN:
{
<code : ("-")?(["A"-"Z", "0"-"9"])+ >
| <op : ("+"|"/") >
| <not : ("-") >
| <lparenthesis : ("(") >
| <rparenthesis : (")") >
}
void expression() :
{
}
{
negated_expression() | parenthesis_expression() | LOOKAHEAD(2) operator_expression() | <code>
}
void negated_expression() :
{
}
{
<not>parenthesis_expression()
}
void parenthesis_expression() :
{
}
{
<lparenthesis>expression()<rparenthesis>
}
void operator_expression() :
{
}
{
<code><op>expression()
}
编辑 - 2009 年 11 月 16 日
现在我尝试了 ANTLR。
我更改了一些术语以更好地匹配我的问题域。我想出了以下代码(使用本网站上的答案),它现在似乎可以完成工作:
grammar Code;
CODE : ('A'..'Z'|'0'..'9')+;
OP : '+'|'/';
start : terms EOF;
terms : term (OP term)*;
term : '-'? CODE
| '-'? '(' terms ')';
顺便说一句...ANTLRWORKS 是一个很棒的调试/可视化工具!对我帮助很大。
附加信息
上面的代码匹配如下内容:
(-Z19+-Z07+((FV+((M005+(M272/M276))/((M278/M273/M642)+-M005)))/(FW+(M005+(M273/M278/M642)))))+(-Z19+-Z07+((FV+((M005+(M272/M276))/((M278/M273/M642/M651)+-M005)))/(FW+(M0))))
最佳答案
kgregory 说的是正确答案。如果您使用 DEBUG_PARSER 选项构建语法然后运行它,您可以看到这一点:
$ javacc -debug_parser -output_directory=com/testing/ CodeParser.jj && javac com/testing/*.java && java -cp . com.testing.CodeParser Java Compiler Compiler Version 5.0 (Parser Generator) (type "javacc" with no arguments for help) Reading from file CodeParser.jj . . . File "TokenMgrError.java" is being rebuilt. File "ParseException.java" is being rebuilt. File "Token.java" is being rebuilt. File "SimpleCharStream.java" is being rebuilt. Parser generated successfully. Call: expression Call: operator_expression Consumed token: <<code>: "A" at line 1 column 1> Consumed token: <<op>: "+" at line 1 column 2> Call: expression Call: operator_expression Consumed token: <<code>: "BC" at line 1 column 3> Consumed token: <<op>: "+" at line 1 column 5> Call: expression Call: negated_expression Consumed token: <"-" at line 1 column 6> Call: parenthesis_expression Consumed token: <"(" at line 1 column 7> Call: expression Call: operator_expression Consumed token: <<code>: "2XXL" at line 1 column 8> Consumed token: <<op>: "+" at line 1 column 12> Call: expression Call: operator_expression Consumed token: <<code>: "A" at line 1 column 13> Consumed token: <<op>: "/" at line 1 column 14> Call: expression Consumed token: <<code>: "-B" at line 1 column 15> Return: expression Return: operator_expression Return: expression Return: operator_expression Return: expression Consumed token: <")" at line 1 column 17> Return: parenthesis_expression Return: negated_expression Return: expression Return: operator_expression Return: expression Return: operator_expression Return: expression
看到了吗?最后消耗的 token 是倒数第二个字符 - 倒数第二个右括号。
如果您想要异常(exception),再次像 kgregory 所说的那样,您可以添加一个名为"file"或“数据”或其他名称的新顶级产品,并以 token 结尾。这样任何像这样的悬空括号都会导致错误。这是执行此操作的语法:
options { STATIC=false; } PARSER_BEGIN(CodeParser) package com.testing; import java.io.StringReader; import java.io.Reader; public class CodeParser { public CodeParser(String s) { this((Reader)(new StringReader(s))); } public static void main(String args[]) { try { /** String has one open, but two closing parenthesis --> should produce parse error */ String s = "A+BC+-(2XXL+A/-B))"; CodeParser parser = new CodeParser(s); parser.file(); } catch(Exception e) { e.printStackTrace(); } } } PARSER_END(CodeParser) TOKEN: { <code : ("-")?(["A"-"Z", "0"-"9"])+ > | <op : ("+"|"/") > | <not : ("-") > | <lparenthesis : ("(") > | <rparenthesis : (")") > } void file() : {} { expression() <EOF> } void expression() : { } { negated_expression() | parenthesis_expression() | LOOKAHEAD(2) operator_expression() | <code> } void negated_expression() : { } { <not>parenthesis_expression() } void parenthesis_expression() : { } { <lparenthesis>expression()<rparenthesis> } void operator_expression() : { } { <code><op>expression() }
和一个样本运行:
$ javacc -debug_parser -output_directory=com/testing/ CodeParser.jj && javac com/testing/*.java && java -cp . com.testing.CodeParser Java Compiler Compiler Version 5.0 (Parser Generator) (type "javacc" with no arguments for help) Reading from file CodeParser.jj . . . File "TokenMgrError.java" is being rebuilt. File "ParseException.java" is being rebuilt. File "Token.java" is being rebuilt. File "SimpleCharStream.java" is being rebuilt. Parser generated successfully. Call: file Call: expression Call: operator_expression Consumed token: <<code>: "A" at line 1 column 1> Consumed token: <<op>: "+" at line 1 column 2> Call: expression Call: operator_expression Consumed token: <<code>: "BC" at line 1 column 3> Consumed token: <<op>: "+" at line 1 column 5> Call: expression Call: negated_expression Consumed token: <"-" at line 1 column 6> Call: parenthesis_expression Consumed token: <"(" at line 1 column 7> Call: expression Call: operator_expression Consumed token: <<code>: "2XXL" at line 1 column 8> Consumed token: <<op>: "+" at line 1 column 12> Call: expression Call: operator_expression Consumed token: <<code>: "A" at line 1 column 13> Consumed token: <<op>: "/" at line 1 column 14> Call: expression Consumed token: <<code>: "-B" at line 1 column 15> Return: expression Return: operator_expression Return: expression Return: operator_expression Return: expression Consumed token: <")" at line 1 column 17> Return: parenthesis_expression Return: negated_expression Return: expression Return: operator_expression Return: expression Return: operator_expression Return: expression Return: file com.testing.ParseException: Encountered " ")" ") "" at line 1, column 18. Was expecting: <EOF> at com.testing.CodeParser.generateParseException(CodeParser.java:354) at com.testing.CodeParser.jj_consume_token(CodeParser.java:238) at com.testing.CodeParser.file(CodeParser.java:34) at com.testing.CodeParser.main(CodeParser.java:22)
瞧!一个异常(exception)。
关于JavaCC 问题 - 生成的代码没有找到所有解析错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/1721534/