What Is Departure Betwixt Hashmap Too Hashtable Inwards Java?

HashMap vs Hashtable inwards Java
Though both Hashtable together with HashMap are data-structure based upon hashing together with implementation of Map interface, the original departure betwixt them is that HashMap is non thread-safe but Hashtable is thread-safe. Which agency you lot cannot utilisation HashMap inwards multi-threaded Java application without external synchronization. Another departure is HashMap allows 1 naught fundamental together with naught values but Hashtable doesn't allow naught fundamental or values. Also, thread-safety of the hash tabular array is achieved using internal synchronization, which makes it slower than HashMap. By the way, difference betwixt HashMap together with Hashtable inwards Java is 1 of the oft asked inwards marrow Java interviews to banking concern gibe whether the candidate understands right usage of collection classes together with aware of choice solutions available.

Along alongside How HashMap internally industrial plant inwards Java together with ArrayList vs Vector, this  is 1 of the oldest questions from Collection framework inwards Java. Hashtable is a legacy Collection class together with it's in that place inwards Java API from a long fourth dimension but it got refactored to implement Map interface inwards Java iv together with from in that place Hashtable became role of Java Collection framework.

Hashtable vs HashMap in Java is thence pop a enquiry that it tin locomote yesteryear whatsoever listing of Java Collection interview Question. You only can't afford non to laid HashMap vs Hashtable before going to whatsoever Java programming interview. In this Java article, nosotros volition non exclusively run into to a greater extent than or less of import differences betwixt HashMap together with Hashtable but besides to a greater extent than or less similarities betwixt these ii collection classes.  Though for consummate preparation,

Let's showtime run into How dissimilar they are:

Difference betwixt HashMap together with Hashtable inwards Java

Both HashMap together with Hashtable implements Map interface but in that place is to a greater extent than or less pregnant departure betwixt them which is of import to recall earlier deciding whether to utilisation HashMap or Hashtable inwards Java. Some of them are thread-safety, synchronization, together with speed. hither are those differences :

1.The HashMap class is roughly equivalent to Hashtable, except that it is non-synchronized together with permits nulls. (HashMap allows naught values equally fundamental together with value whereas Hashtable doesn't allow nulls).

2. One of the major differences betwixt HashMap together with Hashtable is that HashMap is non-synchronized whereas Hashtable is synchronized, which agency Hashtable is thread-safe together with tin live on shared betwixt multiple threads but HashMap can non live on shared betwixt multiple threads without proper synchronization. Java v introduces ConcurrentHashMap which is an choice of Hashtable together with provides ameliorate scalability than Hashtable inwards Java.

3. Another pregnant departure betwixt HashMap vs Hashtable is that Iterator in the HashMap is  a fail-fast iterator  spell the enumerator for the Hashtable is non together with throw ConcurrentModificationException if whatsoever other Thread modifies the map structurally  yesteryear adding or removing whatsoever chemical constituent except Iterator's ain remove() method. But this is non a guaranteed direct together with volition live on done yesteryear JVM on best effort. This is besides an of import difference betwixt Enumeration together with Iterator inwards Java.

4. One to a greater extent than notable difference betwixt Hashtable and HashMap is that because of thread-safety together with synchronization Hashtable is much slower than HashMap if used inwards Single threaded environment. So if you lot don't demand synchronization together with HashMap are exclusively used yesteryear 1 thread, it outperforms Hashtable inwards Java.

5. HashMap does non guarantee that the enterprise of the map volition stay constant over time.

If you lot are preparing this enquiry equally role of your Java interview preparation,  I advise preparing every of import theme equally given in Programming Interviews Exposed. It covers basics, marrow java, threads, a framework similar Spring together with Hibernate together with many others fundamental topics.

HashMap together with Hashtable : Federal Reserve notation on Some Important Terms

1)Synchronized agency exclusively 1 Thread tin modify a hash tabular array at 1 betoken of time. Basically, it agency that whatsoever thread earlier performing an update on a Hashtable will convey to larn a lock on the object spell others volition await for the lock to live on released.

2) Fail-safe is relevant from the context of iterators. If an Iterator or ListIterator has been created on a collection object together with another thread tries to modify the collection object "structurally", a concurrent change exception volition live on thrown. It is possible for other threads though to invoke "set" method since it doesn't modify the collection "structurally". However, if prior to calling "set", the collection has been modified structurally, "IllegalArgumentException" volition live on thrown.

3) Structurally change agency deleting or inserting chemical constituent which could effectively alter the construction of the map.

HashMap tin live on synchronized by

Map one thousand = Collections.synchronizeMap(hashMap);

In Summary, in that place are significant differences betwixt Hashtable together with HashMap inwards Java e.g. thread-safety together with speed together with based upon that exclusively utilisation Hashtable if you lot absolutely demand thread-safety if you lot are running Java v reckon using ConcurrentHashMap in Java.

Further Learning
Java In-Depth: Become a Complete Java Engineer
tutorial)
How to form an ArrayList inwards ascending together with descending enterprise inwards Java? (tutorial)

Difference betwixt ArrayList together with HashSet inwards Java? (answer)
The departure betwixt TreeMap together with TreeSet inwards Java? (answer)
The departure betwixt HashMap together with ConcurrentHashMap inwards Java? (answer)
The departure betwixt HashMap together with LinkedHashMap inwards Java? (answer)
The departure betwixt Hashtable together with HashMap inwards Java? (answer)
The departure betwixt HashSet together with TreeSet inwards Java? (answer)
The departure betwixt ArrayList together with LinkedList inwards Java? (answer)
The departure betwixt Vector together with ArrayList inwards Java? (answer)
Difference betwixt EnumMap together with HashMap inwards Java

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