Question

The regular expression, specifically for negative lookahead patterns, does not seem to work properly in Android 2.1 code.

See example below:

private String parseString(String regex, String raw) {
    StringBuffer sb = new StringBuffer();
    Matcher m = Pattern.compile(regex).matcher(raw);
    m.matches();
    if (m.find()) sb.append(m.group()); 
    return sb.toString();
}

// Using the helper method above:
// Looking for 4-digit numeric strings within a text
String regex = "(\\d{4})(?!\\d)";
String text = "Looking for a 4-digit string 1234 in here!";
Log.i("Test", "[" + parseString(regex, text) + "]");

On Android 2.1, the result comes as:

I/Test (  451): []

On Android 2.2, it is:

I/Test (  451): [1234]

Does anyone know the reason for this?

Answer 1

There is a bug in Android’s regular expression, specifically for negative lookahead patterns.

Official ticket was created and fixed in Android 2.2 (Froyo):
http://code.google.com/p/android/issues/detail?id=17159

The solution:

(a) Do not use Android 2.1 if you need this; or

(b) Rebuild your regex without negative pattern (might get dirtier, but should work)