- Several classes provide implementations of the map interfaces. The classes that can be used for the maps are as shown below.
- Abstract map, hash map, tree map, weak hash map, linked hash map, identify hash map.
- The map class hierarchy is,
Hashmap Treemap weak hashmap identify hashmap
The hashmap class:
- The hash map class uses a hash table to implements the map interface.
- This allows the execution time of basic operations, such as get () and put (), to remain constant even for large sets.
The treemap classes:
- The tree map class implements the map interface by using a tree.
- A tree map provides an efficient means of storing key/values pairs in the sorted order and allows rapid retrieval.
- A tree map guarantees that its element will be sorted in ascending key order.
The linkedhashmap classes:
- This class extends maps.
- Linked hash map maintains a linked list of the entries in the map, in the order in which they were inserted. Thus, when iterating a linked hash map, the elements will be returned in the order in which they were inserted.
- We can also create a linked hash map that returns its elements in the order in which they were last accessed.
The identify hash map class:
- This class extends hash abstract map.
- It is similar to the hash map except that it uses reference equality when comparing elements.
- The java2 documentation explicitly states that identify hash map is not for general use.