在ConcurrentHashMap内部将条目添加到LinkedList无效

Question

I have a ConcurrentHashMap that contains a string as a key and LinkedList as a value. The size of the list should not be more than 5. I am trying to add some elements to the list but when I print out the Map I see only the last added element. Here is my code:

private ConcurrentHashMap<String, LinkedList<Date>> userDisconnectLogs = new ConcurrentHashMap<String, LinkedList<Date>>();

public void addNewDateEntry(String userId, LinkedList<Date> timeStamps) {
    if (timeStamps.size() >= 5) {
        timeStamps.poll();
        timeStamps.add(new Date());
        userDisconnectLogs.put(userId, timeStamps);
    } else {
        timeStamps.add(new Date());
        userDisconnectLogs.put(userId, timeStamps);
    }

    for (Entry<String, LinkedList<Date>> entry : userDisconnectLogs
            .entrySet()) {
        String key = entry.getKey().toString();
        ;
        LinkedList<Date> value = entry.getValue();
        System.out.println("key: " + key + " value: " + value.size());
    }
}

Thank you!

Answer 1

Here for hashMap key must be unique. And from this code it seems key is always same so all the time it will overrite the data.