Although each Hashtable and HashMap are data-structure based mostly upon hashing and implementation of Map interface, the principle distinction between them is that HashMap will not be thread-safe however Hashtable is thread-safe. This implies you can not use HashMap in a multi-threaded Java utility 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 continuously requested in core Java interviews to test whether or not the candidate understands the proper utilization of assortment courses 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 acquired refactored to implement Map interface in Java 4 and from there Hashtable turned a part of the Java Assortment framework.
Hashtable vs HashMap in Java is so well-liked a query that it could high any checklist of Java Assortment Interview Questions. You simply cannot afford to arrange HashMap vs Hashtable earlier than going to any Java programming interview. On this Java article, we is not going to solely see some necessary variations between HashMap and Hashtable but in addition some similarities between these two assortment courses. 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 necessary 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 velocity. 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 will not be and throw ConcurrentModificationException if some other Thread modifies the map structurally by including or eradicating any factor besides Iterator‘s personal take away() methodology. However this isn’t a assured conduct and can be accomplished by JVM on greatest effort. That is additionally an necessary 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 way slower than HashMap if utilized in Single threaded setting. So if you happen to 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 getting ready this query as a part of your Java interview preparation, I counsel getting ready each necessary matter as given in Programming Interviews Uncovered. It covers fundamentals, core java, threads, a framework like Spring and Hibernate and lots of others key matters.
HashMap and Hashtable : word 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 item whereas others will look ahead to the lock to be launched.
3) Structurally modification means deleting or inserting factor which may successfully change the construction of the map.
HashMap will 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 velocity and based mostly upon that solely use Hashtable if you happen to completely want thread-safety in case you are working Java 5 think about using ConcurrentHashMap in Java.
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Distinction between EnumMap and HashMap in Java
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