In last article, I have showed you how to update value in HashMap and today we'll learn about how to update value in a ConcurrentHashMap. Some of you may question, can we use the same technique we used to update a value in HashMap here? well, you can but you need to keep in mind the difference between an HashMap and a ConcurrentHashMap. The HashMap is only meant to be updated by one thread at a time, hence you don't need to pay any attention to thread-safety or concurrency, but ConcurrentHashMap can be updated by multiple threads at the same time, hence you need to pay special attention.