Difference between hashtable and hash map

[Pushker Chaubey]

Why was HashMap introduced when we already had Hashtable. What are differences between the two?

[Jesper de Jong]

Lookup the description of Hashtable and HashMap in the API documentation.

The main difference is that Hashtable is synchronized and HashMap is not. Because of that, HashMap might be slightly faster, because it doesn't have the overhead of synchronization.

Hashtable is an old class from before the time of Java 1.2. In Java 1.2, a new collections API was added. See: The Collections Framework, especially the Design FAQ might be interesting if you want to know why it was designed as it is.

[Jaikiran Pai]

Apart from the synchronized part, one other difference is mentioned in the Javadocs of HashMap. Here's an extract:

The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls.

[ December 11, 2006: Message edited by: Jaikiran Pai ]

[Paul Sturrock]

Not an advanced question. Moving...

[Neerav Narielwala]

Hashmap is not synchronised, and allows null for key and values where as Hashtable is synchronised and does not allow null values. The elements may not be in an order in the case of hashmap.

[Prabhu Venkatachalam]

The elements may not be in an order in the case of hashmap

Even with HashTable, ordering and sorting is not guaranteed.