FULL PRODUCT VERSION :
java version "1.6.0_11"
Java(TM) SE Runtime Environment (build 1.6.0_11-b03)
Java HotSpot(TM) Client VM (build 11.0-b16, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
See steps to reproduce and run the code snippet.  The thread will hang in an infinite loop.

The regular expression pattern is invalid as far as I know; I don't think the "?+" is correct.  I would think that Pattern.compile() should be throwing an exception.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run this simple 2-line code snippet (full class below).

Pattern pattern = Pattern.compile("(([0-9A-Z]+)([_]?+)*)*");
pattern.matcher("FOOOOO_BAAAR_FOOOOOOOOO_BA_ ").matches();


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Should not hang.
ACTUAL -
VM hangs in an infinite loop.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.regex.Pattern;

public class RegexTest {
    public static void main(String[] args) {
        Pattern pattern = Pattern.compile("(([0-9A-Z]+)([_]?+)*)*");
        pattern.matcher("FOOOOO_BAAAR_FOOOOOOOOO_BA_ ").matches();
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Correct the regex.