Question

I use javacc 5.0 to generate a json parser with the grammar file: https://github.com/inqwell/json/blob/master/src/main/javacc/com/inqwell/json/JSON.jj

But there are some errors in the generated java source code.

char escape = '\u005c\u005c';

and

switch(echar)
{
  case 'n':
    buf.append(System.getProperties().get("line.separator")); to++;
    break;

  case 'r':  buf.append('\u005cr'); to++; break;
  case 't':  buf.append('\u005ct'); to++; break;
  case 'b':  buf.append('\u005cb'); to++; break;
  case 'f':  buf.append('\u005cf'); to++; break;
  case '\u005c\u005c': buf.append('\u005c\u005c'); to++; break;
  case '"':  buf.append('"');  to++; break;
  case '\u005c'': buf.append('\u005c''); to++; break;
  case '\u005cr': to++; if (to < len && s.charAt(to) == '\u005cn') to++; break;
  case '\u005cn': to++; break;
}

And in the grammer file, they are:

char escape = '\\';

And

switch(echar)
{
  case 'n':
    buf.append(System.getProperties().get("line.separator")); to++;
    break;

  case 'r':  buf.append('\r'); to++; break;
  case 't':  buf.append('\t'); to++; break;
  case 'b':  buf.append('\b'); to++; break;
  case 'f':  buf.append('\f'); to++; break;
  case '\\': buf.append('\\'); to++; break;
  case '"':  buf.append('"');  to++; break;
  case '\'': buf.append('\''); to++; break;
  case '\r': to++; if (to < len && s.charAt(to) == '\n') to++; break;
  case '\n': to++; break;
}

These case chars should not be escaped, but how to do it?

---

update

The code can’t be compiled in my IDEA, please see my screenshot:

Answer 1

There is no error in the generated code. The literals '\\' and '\u005c\u005c' mean the same thing in Java. The reason is that unicode escapes are processed first and other escape sequences are processed later. See section 3.2 of the JLS (3rd edition) http://docs.oracle.com/javase/specs/jls/se5.0/html/lexical.html

---

Edit: The following was added in response to Freewind’s comment

theo-laptop:src theo$ javacc JSON.jj
Java Compiler Compiler Version 5.0 (Parser Generator)
(type "javacc" with no arguments for help)
Reading from file JSON.jj . . .
Note: UNICODE_INPUT option is specified. Please make sure you create the parser/lexer using a Reader with the correct character encoding.
File "TokenMgrError.java" is being rebuilt.
File "ParseException.java" is being rebuilt.
File "Token.java" is being rebuilt.
File "JavaCharStream.java" is being rebuilt.
Parser generated successfully.
theo-laptop:src theo$ fgrep \\u005c JSON.java
char escape = '\u005c\u005c';
  case 'r': buf.append('\u005cr'); to++; break;
  case 't': buf.append('\u005ct'); to++; break;
  case 'b': buf.append('\u005cb'); to++; break;
  case 'f': buf.append('\u005cf'); to++; break;
  case '\u005c\u005c': buf.append('\u005c\u005c'); to++; break;
  case '\u005c'': buf.append('\u005c''); to++; break;
  case '\u005cr': to++; if (to < len && s.charAt(to) == '\u005cn') to++; break;
  case '\u005cn': to++; break;
theo-laptop:src theo$ javac JSON.java
theo-laptop:src theo$ javac -version
javac 1.7.0_07