How do ConcurrentHashMap and Hashtable differ in Java?

What are the main differences between ConcurrentHashMap and Hashtable in Java?

ConcurrentHashMap is designed for concurrent access, allowing multiple threads to read and write without locking the entire map, while Hashtable locks the entire map for each operation, making it less efficient in multi-threaded environments.

Can you explain how the locking mechanism works in both?

Sure! Hashtable uses a single lock for the entire map, which means only one thread can access it at a time. In contrast, ConcurrentHashMap uses a segmented locking mechanism, allowing multiple threads to access different segments simultaneously.

Which one should I use for a multi-threaded application?

For a multi-threaded application, ConcurrentHashMap is generally preferred due to its better performance and scalability under concurrent access.

Are there any scenarios where Hashtable might still be useful?

Yes, Hashtable can be useful in legacy code or when thread safety is required but concurrency is not a concern, as it provides a simpler implementation.