The difference between Java HashMap and Hashtable

HashMap is a lightweight implementation of Hashtable (non-thread-safe implementation), they all complete the map interface, the main difference is that the HASHMAP allows null (NULL) key value (key), because of non-thread security, the efficiency may be higher than Hashtable.

HashMap allows NULL to be used as a entry key or value, and Hashtable is not allowed.

HashMap hashtable contains method removed, changed to Containsvalue and ContainsKey. Because the contains method is easy to cause misunderstanding.

Hashtable inherits from the dictionary class, and HashMap is an implementation of the map interface introduced by Java1.2.

The biggest difference is that the Hashtable method is synchronize, and HashMap is not, when multiple threads access Hashtable, they do not need to synchronize their methods, and HashMap must provide external synchronization.

The Hash/rehash algorithms used by Hashtable and HashMap are probably the same, so there is no big difference in performance.

The difference between Java HashMap and Hashtable