Difference between ConcurrentHashMap and Hashtable
Both ConcurrentHashMap and Hashtable are Collection classes for storing key value pairs and they both provide fast element search with a supplied key. They have much in common. However, we will not discuss the similarities between them here, instead we will focus on the differences between them.
ConcurrentHashMap and Hashtable are both thread safe. But the mechanism for thread safe is different between them. Hashtable is synchronized, it utilizes the synchronization mechanism; while ConcurrentHashMap uses segmentation to lock the data, it uses concurrent locks operations for thread safety instead of synchronized.
Since ConcurrentHashMap introduced concept of segmentation , how large it becomes only certain part of it get locked to provide thread safety so many other readers can still access map without waiting for iteration to complete.
So if you want to store large amount of data in a multithreaded program, you should consider to choose ConcurrentHashMap.