What is differences between HashMap and Hashtable in Java?

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There are several differences between HashMap and Hashtable in Java:

  1. Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
  2. Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.

Differences between HashMap and Hashtable in Java?

HashMapHashtable
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.

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