What are the differences between a HashMap and a Hashtable in Java?

Question

What are the differences between a HashMap and a Hashtable in Java? Which is more efficient for non-threaded applications?

Uday Dodiya · Answer

Hi Jaya There are several differences between HashMap and Hashtable in Java: Hashtable is synchronized whereas HashMap is not. This makes HashMap better for non-threaded applications as unsynchronized Objects typically perform better than synchronized ones. Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values. One of HashMap's subclasses is LinkedHashMap  so if you'd want predictable iteration order (which is insertion order by default) you could easily swap out the HashMap for a LinkedHashMap . This wouldn't be as easy if you were using Hashtable . Since synchronization is not an issue for you I'd recommend HashMap. If synchronization becomes an issue you may also look at ConcurrentHashMap

Amit Kumar · Answer

Hi  Differences are. S. No. Hashmap Hashtable 1. No method is synchronized. Every method is synchronized. 2. Multiple threads can operate simultaneously and hence hashmap’s object is not thread-safe. At a time only one thread is allowed to operate the Hashtable’s object. Hence it is thread-safe. 3. Threads are not required to wait and hence relatively performance is high. It increases the waiting time of the thread and hence performance is low. 4. Null is allowed for both key and value. Null is not allowed for both key and value. Otherwise we will get a null pointer exception. 5. It is introduced in the 1.2 version. It is introduced in the 1.0 version. 6. It is non-legacy. It is a legacy. For more detail https://www.geeksforgeeks.org/differences-between-hashmap-and-hashtable-in-java/#:~:text=Hashmap%20vs%20Hashtable&text=It%20is%20thread%2Dsafe%20andthread%20synchronization%20is%20not%20needed.

Dhanush K · Answer

Hashtable is synchronized. If a thread-safe implementation is not needed it is recommended to use HashMap in place of Hashtable . If a thread-safe highly-concurrent implementation is desired then it is recommended to use ConcurrentHashMap in place of Hashtable .