Differences between ConcurrentHashMap and HashTable

ConcurrentHashMap and Hashtable are both classes in Java that provide thread-safe implementations of the Map interface. However, there are some key differences between the two:

• Synchronization: Hashtable is synchronized, meaning all its methods are thread-safe. On the other hand, ConcurrentHashMap provides better performance by allowing multiple threads to access the map concurrently, while still ensuring thread-safety.
• Performance: ConcurrentHashMap provides better performance compared to Hashtable due to its ability to allow multiple threads to access the map concurrently.
• Null keys/values: Hashtable does not allow null keys or values, while ConcurrentHashMap allows one null key and any number of null values.
• Iterators: The iterators returned by Hashtable are weakly consistent, meaning they may or may not reflect the current state of the map. The iterators returned by ConcurrentHashMap, on the other hand, are weakly consistent, meaning they may reflect some, but not necessarily all, changes made to the map while the iterator is active.

In conclusion, if you need a thread-safe Map implementation and don’t need to allow null keys/values, you can use either Hashtable or ConcurrentHashMap. If performance is a concern, ConcurrentHashMap is the better choice due to its ability to allow multiple threads to access the map concurrently.