Java Collection Class learning notes (Map Collection)

Map is used to save data that has mappings, so there are two sets of data stored in the Map collection, a set of keys to hold the map, and a set of keys to hold the value corresponding to the key.

The map key does not allow duplication.

HashMap and Hashtable are typical implementations of map interfaces, and their relationships are similar to those of ArrayList and vectors.

The difference between HashMap and Hashtable:

• Hashtable is a thread-safe map implementation, but HashMap is a thread-insecure implementation.
• Hashtable is not allowed to use NULL as key and Value,hashmap.

Linkedhashmap is a subclass of HashMap and also uses a doubly linked list to maintain the order of Key-value.

Java Collection Class learning notes (Map Collection)