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Although each Hashtable and HashMap are data-structure primarily based upon hashing and implementation of Map interface, the principle distinction between them is that HashMap is just not thread-safe however Hashtable is thread-safe. This implies you can not use HashMap in a multi-threaded Java software with out exterior synchronization. One other distinction is HashMap permits one null key and null values however Hashtable would not permit null key or values. Additionally, the thread-safety of the hash desk is achieved utilizing inner synchronization, which makes it slower than HashMap.
By the way in which, the distinction between HashMap and Hashtable in Java is among the incessantly requested in core Java interviews to test whether or not the candidate understands the right utilization of assortment lessons and conscious of other options accessible.
Together with How HashMap internally works in Java and ArrayList vs Vector, this is among the oldest questions from the Assortment framework in Java. Hashtable is a legacy Assortment class and it is there in Java API for a very long time nevertheless it received refactored to implement Map interface in Java 4 and from there Hashtable grew to become a part of the Java Assortment framework.
Hashtable vs HashMap in Java is so in style a query that it may prime any checklist of Java Assortment Interview Questions. You simply cannot afford to organize HashMap vs Hashtable earlier than going to any Java programming interview. On this Java article, we won’t solely see some essential variations between HashMap and Hashtable but in addition some similarities between these two assortment lessons. Although for full preparation,
Let’s first see How totally different they’re:
Distinction between HashMap and Hashtable in Java
Each HashMap and Hashtable implements Map interface however there may be some important distinction between them which is essential to recollect earlier than deciding whether or not to make use of HashMap or Hashtable in Java. A few of them are thread-safety, synchronization, and pace. listed below are these variations :
3. One other important distinction between HashMap vs Hashtable is that Iterator within the HashMap is a fail-fast iterator whereas the enumerator for the Hashtable is just not and throw ConcurrentModificationException if some other Thread modifies the map structurally by including or eradicating any component besides Iterator‘s personal take away() technique. However this isn’t a assured habits and might be carried out by JVM on greatest effort. That is additionally an essential distinction between Enumeration and Iterator in Java.
4. Another notable distinction between Hashtable and HashMap is that due to thread-safety and synchronization Hashtable is far slower than HashMap if utilized in Single threaded setting. So for those who do not want synchronization and HashMap are solely utilized by one thread, it outperforms Hashtable in Java.
5. HashMap doesn’t assure that the order of the map will stay fixed over time.
If you’re making ready this query as a part of your Java interview preparation, I recommend making ready each essential subject as given in Programming Interviews Uncovered. It covers fundamentals, core java, threads, a framework like Spring and Hibernate and plenty of others key subjects.
HashMap and Hashtable : observe on Some Vital Phrases
1)Synchronized means just one Thread can modify a hash desk at one level of time. Mainly, it signifies that any thread earlier than performing an replace on a Hashtable must purchase a lock on the thing whereas others will await the lock to be launched.
3) Structurally modification means deleting or inserting component which may successfully change the construction of the map.
HashMap may be synchronized by
Map m = Collections.synchronizeMap(hashMap);
Additionally, right here is yet another desk which reveals extra variations between HashMap and Hashtable in Java:
In Abstract, there are important variations between Hashtable and HashMap in Java e.g. thread-safety and pace and primarily based upon that solely use Hashtable for those who completely want thread-safety if you’re operating Java 5 think about using ConcurrentHashMap in Java.
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