FULL PRODUCT VERSION :
java version "1.5.0_04"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_04-b05)
Java HotSpot(TM) Client VM (build 1.5.0_04-b05, mixed mode, sharing)

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

EXTRA RELEVANT SYSTEM CONFIGURATION :
This was opened by another individual as 6295722, however, his was only intermittently reproducible and was closed by Sun as not able to reproduce.

My test fails *every time* within a second of starting the program.

Sun team says they tested 6295722 for 100hours on a 4CPU machine with no failure.
My system is a 3.2Ghz HT single-CPU system. I would suggest testing on a high-mhz Intel box. (in the case the 4-cpu machine was a sparc /w a slower mhz rating or is simply a platform issue - i know it's rare, but it could be a factor)

A DESCRIPTION OF THE PROBLEM :
DateFormat.format fails with an ArrayIndexOutOfBoundsException under heavy load.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run test case below.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No failures, should run continuously.
ACTUAL -
java.lang.ArrayIndexOutOfBoundsException: -2147483648
at java.text.SimpleDateFormat.subFormat(SimpleDateFormat.java:934)
at java.text.SimpleDateFormat.format(SimpleDateFormat.java:806)
at java.text.SimpleDateFormat.format(SimpleDateFormat.java:778)
at java.text.DateFormat.format(DateFormat.java:314)
at test$1.run(test.java:24)

ERROR MESSAGES/STACK TRACES THAT OCCUR :
java.lang.ArrayIndexOutOfBoundsException: -2147483648
at java.text.SimpleDateFormat.subFormat(SimpleDateFormat.java:934)
at java.text.SimpleDateFormat.format(SimpleDateFormat.java:806)
at java.text.SimpleDateFormat.format(SimpleDateFormat.java:778)
at java.text.DateFormat.format(DateFormat.java:314)
at test$1.run(test.java:24)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public class test {
    private static final DateFormat dateFormat = new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss zzz");
    public static void main(String[] args) throws Exception {
        for (int c=0; c<3; c++) {
            Thread th = new Thread() {
                public void run() {
                    Random rand = new Random();
                    while (true) {
                        Date date = new Date(rand.nextLong());
                        try {
                            dateFormat.format(date);
                        } catch (RuntimeException e) {
                            e.printStackTrace();
                            System.exit(1);
                        }
                    }
                }
            };
            th.start();
        }
    }
}

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

CUSTOMER SUBMITTED WORKAROUND :
Can use separate instances of DateFormat, however this is very expensive in instances and there are some places we cannot control it's use. (3rd party)
Instance-saving options such as pooling would be unnecessarily complex.