Difference between HashMap and HashTable? Compare Hashtable vs HashMap

Both Hashtable & HashMap provide key-value access to data. The Hashtable is one of the original collection classes in Java (also called as legacy classes). HashMap is part of the new Collections Framework, added with Java 2, v1.2. There are several differences between HashMap and Hashtable in Java as listed below

  • The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. (HashMap allows null values as key and value whereas Hashtable doesn’t allow nulls).
  • HashMap does not guarantee that the order of the map will remain constant over time. But one of HashMap’s subclasses is LinkedHashMap, so in the event that you’d want predictable iteration order (which is insertion order by default), you can easily swap out the HashMap for a LinkedHashMap. This wouldn’t be as easy if you were using Hashtable.
  • HashMap is non synchronized whereas Hashtable is synchronized.
  • Iterator in the HashMap is fail-fast while the enumerator for the Hashtable isn’t. So this could be a design consideration.