Java / Map and its implementations
List the differences between HashTable and HashMap in Java collections.
| HashMap. | HashTable. |
| HashMap is not synchronized and therefore it is not thread safe. | HashTable is internally synchronized and therefore it is thread safe. |
| HashMap allows maximum one null key and any number of null values. | HashTable does not allow null keys and null values. |
| Iterators returned by the HashMap are fail-fast in nature. | Enumeration returned by the HashTable are fail-safe in nature. |
| HashMap extends AbstractMap class. | HashTable extends Dictionary class. |
| HashMap returns only iterator to traverse. | HashTable returns both Iterator as well as Enumeration for traversal. |
| HashMap is fast. | HashTable is slow. |
| HashMap is not a legacy class. | HashTable is a legacy class. |
HashMap is preferred in single threaded applications. If you want to use HashMap in multi threaded application, wrap it using Collections. synchronizedMap() method. | Although HashTable is there to use in multi threaded applications, now a days it is not at all preferred. Because, ConcurrentHashMap is better option than HashTable. |
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