My regex is causing a stack overflow in Java; what am I missing?

Question

I am attempting to use a regular expression with Scanner to match a string from a file. The regex works with all of the contents of the file except for this line:

Answer 1

As the others have said, your regex is much less efficient than it should be. I'd take it a step further and use possessive quantifiers:

"^([a-zA-Z]++) *+= *+\"([^\"]++)\"$"

But the way you're using the Scanner doesn't make much sense, either. There's no need to use findInLine(".*") to read the line; that's what nextLine() does. And you don't need to create another Scanner to apply your regex; just use a Matcher.

static final Pattern ANIMAL_INFO_PATTERN = 
    Pattern.compile("^([a-zA-Z]++) *+= *+\"([^\"]++)\"$");

...

  Matcher lineMatcher = ANIMAL_INFO_PATTERN.matcher("");
  while (scanFile.hasNextLine()) {
    String currentLine = scanFile.nextLine();
    if (lineMatcher.reset(currentLine).matches()) {
      matches.put(lineMatcher.group(1), lineMatcher.group(2));
    }
  }

Answer 2

This looks like bug 5050507 . I agree with Asaph that removing the alternation should help; the bug specifically says "Avoid alternation whenever possible". I think you can go probably even simpler:

"^([a-zA-Z]+) *= *\"([^\"]+)"

Answer 3

Try this simplified version of your regex that removes some unnecessary | operators (which might have been causing the regex engine to do a lot of branching) and includes beginning and end of line anchors.

static final String ANIMAL_INFO_REGEX = "^([a-zA-Z]+) *= *\"([a-zA-Z_. ]+)\"$";

Answer 4

read this to understand the problem: http://www.regular-expressions.info/catastrophic.html ... and then use one of the other suggestions