Can a Java HashMap's size() be out of sync with its actual entries' size?

Question

I have a Java HashMap called statusCountMap.
Calling size() results in 30.
But if I count the entries manually, it's 31
This is in one of my TestNG unit tests. These results below are from Eclipse's Display window (type code -> highlight -> hit Display Result of Evaluating Selected Text).

statusCountMap.size()
     (int) 30
statusCountMap.keySet().size()
     (int) 30
statusCountMap.values().size()
     (int) 30
statusCountMap
     (java.util.HashMap) {40534-INACTIVE=2, 40526-INACTIVE=1, 40528-INACTIVE=1, 40492-INACTIVE=3, 40492-TOTAL=4, 40513-TOTAL=6, 40532-DRAFT=4, 40524-TOTAL=7, 40526-DRAFT=2, 40528-ACTIVE=1, 40524-DRAFT=2, 40515-ACTIVE=1, 40513-DRAFT=4, 40534-DRAFT=1, 40514-TOTAL=3, 40529-DRAFT=4, 40515-TOTAL=3, 40492-ACTIVE=1, 40528-TOTAL=4, 40514-DRAFT=2, 40526-TOTAL=3, 40524-INACTIVE=2, 40515-DRAFT=2, 40514-ACTIVE=1, 40534-TOTAL=3, 40513-ACTIVE=2, 40528-DRAFT=2, 40532-TOTAL=4, 40524-ACTIVE=3, 40529-ACTIVE=1, 40529-TOTAL=5}
statusCountMap.entrySet().size()
     (int) 30

What gives ? Anyone has experienced this ?
I'm pretty sure statusCountMap is not being modified at this point.
There are 2 methods (lets call them methodA and methodB) that modify statusCountMap concurrently, by repeatedly calling incrementCountInMap.

private void incrementCountInMap(Map map, Long id, String qualifier) {
    String key = id + "-" + qualifier;
    if (map.get(key) == null) {
        map.put(key, 0);
    }
    synchronized (map) {
        map.put(key, map.get(key).intValue() + 1);
    }
}

methodD is where I'm getting the issue. methodD has a TestNG @dependsOnMethods = { "methodA", "methodB" } so when methodD is executing, statusCountMap is pretty much static already. I'm mentioning this because it might be a bug in TestNG.
I'm using Sun JDK 1.6.0_24. TestNG is testng-5.9-jdk15.jar

Hmmm ... after rereading my post, could it be because of concurrent execution of outside-of-synchronized-block map.get(key) == null & map.put(key,0) that's causing this issue ?

Answer 1

I believe you can achieve this if you modify a key after it is added to a HashMap.

However in your case it appears to be just a case of modifying the same map in two threads without proper synchronization. e.g. in thread A, map.put(key, 0), thread B map.put(key2, 0) can results in a size of 1 or 2. If you do the same with remove you can end up with a size larger than you should.