java tutorial - Difference between HashMap and Hashtable - java programming - learn java - java basics - java for beginners
HashMap and Hashtable both are used to store data in key and value form. Both are using hashing technique to store unique keys.
- But there are many differences between HashMap and Hashtable classes that are given below.
| HashMap | Hashtable |
|---|---|
| 1) HashMap is non synchronized. It is not-thread safe and can't be shared between many threads without proper synchronization code. | Hashtable is synchronized. It is thread-safe and can be shared with many threads. |
| 2) HashMap allows one null key and multiple null values. | Hashtable doesn't allow any null key or value. |
| 3) HashMap is a new class introduced in JDK 1.2. | Hashtable is a legacy class. |
| 4) HashMap is fast. | Hashtable is slow. |
| 5) We can make the HashMap as synchronized by calling this code Map m = Collections.synchronizedMap(hashMap); | Hashtable is internally synchronized and can't be unsynchronized. |
| 6) HashMap is traversed by Iterator. | Hashtable is traversed by Enumerator and Iterator. |
| 7) Iterator in HashMap is fail-fast. | Enumerator in Hashtable is not fail-fast. |
| 8) HashMap inherits AbstractMap class. | Hashtable inherits Dictionary class. |