Difference between HashMap and Hashtable | HashMap Vs Hashtable

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.

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Related posts:

1. How HashMap works in Java
2. Java HashMap put(K key, V value) Example
3. Java HashMap get(Object key) Example
4. Java Hashtable get(Object key) Example

Filed Under: Java, Java InterviewTagged With: difference, hashmap, hashmap and hashtable, hashtable, synchronization, thread-safe