Both the HashMap and Hashtable implement the interface java.util.Map but there are some slight differences which has to be known to write a much efficient code.
- The Most important difference between HashMap and the Hashtable is that Hashtable is synchronized and HashMap is non-synchronized , which means Hashtable is thread-safe and can be shared among multiple threads and you don’t need to worry about the synchronization problems. As only one thread can access the Hashtable at a time whereas Hashmap is not thread-safe and it cannot be shared between threads without synchronization. You can synchronize the HashMap using this below code.
Map m = Collections.synchronizedMap(hashMap);
- HashMap permits one null key and multiple null values whereas the Hashtable will not allow null key or value.
- Since the Hashtable is thread-safe it is comparatively slower than the HashMap in the environment where Synchronization factor is not considered.
- HashMap can be traversed by using the iterator, whereas the Hashtable can be traversed by using enumerator and iterator.
- HashMap inherits AbstractMap class and Hashtable inherits Dictionary class.