Difference between synchronized HashMap and HashTable?

Core Java

Shalini

Asked on December 18, 2014

As we know that we can synchronize Hash Map as Collections.synchronizedMap(map).

HashTable is already synchronized.

So what is difference between synchronized HashMap and HashTable?

clintwelbar

Replied on April 20, 2017

Hashtable is synchronized, whereas HashMap is not synchronized. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform much better than synchronized ones. Synchronized means only a single thread can modify a hashtable at one point of time. Basically, that means any thread before performing an update on a hashtable will have to acquire a lock on the object while others will wait for lock to be released.

clintwelbar

Replied on July 03, 2017

Both HashTable and HashMap implements Map interface but there are some differences between these two. They are:

Thread Safety (synchronized)
Null Keys
Inheritance
Performance
Traverse
Fail-safe
Time Complexity
Legacy

Thread Safety (synchronized)

First and most significant different between Hashtable and HashMap is that, HashMap is not thread-safe (unsynchronized) while Hashtable is a thread-safe (synchronized) collection. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.

Synchronized means only one thread can modify a hash table at one point of time. Basically, it means that any thread before performing an update on a hashtable will have to acquire a lock on the object while others will wait for lock to be released.

You can make the HashMap as thread-safe (synchronized) by calling this code

Map mp = Collections.synchronizedMap(hashMap);