Difference Betwixt Concurrenthashmap, Hashtable As Well As Synchronized Map Inwards Java

ConcurrentHashMap vs Hashtable vs Synchronized Map
Though all iii collection classes are thread-safe in addition to tin move used inwards multi-threaded, concurrent Java application, in that place is a pregnant departure betwixt them, which arise from the fact that how they accomplish their thread-safety. Hashtable is a legacy shape from JDK 1.1 itself, which uses synchronized methods to accomplish thread-safety. All methods of Hashtable are synchronized which makes them quite tiresome due to arguing if a break of thread increases. Synchronized Map is besides non really dissimilar than Hashtable in addition to provides similar functioning inwards concurrent Java programs. The exclusively departure betwixt Hashtable in addition to Synchronized Map is that afterward is non a legacy in addition to you lot tin wind whatsoever Map to create it's synchronized version yesteryear using Collections.synchronizedMap() method.


On the other hand, ConcurrentHashMap is peculiarly designed for concurrent role i.e. to a greater extent than than i thread. By default it simultaneously allows xvi threads to read in addition to write from Map without whatsoever external synchronization. It is besides really scalable because of stripped locking technique used inwards the internal implementation of ConcurrentHashMap class. Unlike Hashtable in addition to Synchronized Map, it never locks whole Map, instead, it divides the map into segments in addition to locking is done on those. Though it performs amend if a break of reader threads are greater than the break of author threads.

To move frank, Collections classes are the pump of Java API though I experience using them judiciously is an art. It's my personal experience where I convey improved the functioning of Java application yesteryear using ArrayList where legacy codes were unnecessarily using Vector etc. Prior Java 5, One of the major drawback of Java Collection framework was a lack of scalability.


In multi-threaded Java application synchronized collection classes similar Hashtable in addition to Vector apace becomes the bottleneck; to address scalability JDK 1.5 introduces simply about expert concurrent collections which are highly efficient for high volume, depression latency organisation electronic trading systems In full general those are the backbone for Concurrent fast access to stored data.


In this tutorial, nosotros volition await on ConcurrentHashMap, Hashtable, HashMap in addition to synchronized Map in addition to come across the departure betwixt ConcurrentHashMap in addition to Hashtable in addition to synchronized Map inwards Java. We convey already discussed simply about key difference betwixt HashMap in addition to Hashtable inwards Java in this spider web log in addition to those volition besides aid you lot to respond this enquiry during interviews.

Why require ConcurrentHashMap in addition to CopyOnWriteArrayList

The synchronized collections classes, Hashtable, in addition to Vector, in addition to the synchronized wrapper classes, Collections.synchronizedMap() in addition to Collections.synchronizedList(), render a basic conditionally thread-safe implementation of Map in addition to List. However, several factors brand them unsuitable for role inwards highly concurrent applications, for example, their unmarried collection-wide lock is an impediment to scalability in addition to it ofttimes becomes necessary to lock a collection for a considerable fourth dimension during iteration to preclude ConcurrentModificationException.

ConcurrentHashMap in addition to CopyOnWriteArrayList implementations render much higher concurrency piece preserving thread safety, amongst simply about shaver compromises inwards their promises to callers. ConcurrentHashMap in addition to CopyOnWriteArrayList are non necessarily useful everywhere you lot mightiness role HashMap or ArrayList, but are designed to optimize specific mutual situations. Many concurrent applications volition practice goodness from their use. 

Difference betwixt ConcurrentHashMap in addition to Hashtable

So what is the departure betwixt Hashtable in addition to ConcurrentHashMap, both tin move used inwards the multithreaded environs but i time the size of Hashtable becomes considerable large functioning degrade because for iteration it has to move locked for a longer duration.

Since ConcurrentHashMap introduced the concept of segmentation, how large it becomes exclusively for certain business office of it instruct locked to render thread security thus many other readers tin all the same access map without waiting for iteration to complete. 

In Summary, ConcurrentHashMap exclusively locked for certain portion of Map piece Hashtable locks sum map piece doing iteration. This volition move clearer yesteryear looking at this diagram which explains the internal working of ConcurrentHashMap inwards Java.

The departure betwixt ConcurrentHashMap in addition to Collections.synchronizedMap

ConcurrentHashMap is designed for concurrency in addition to improve functioning piece HashMap which is non-synchronized yesteryear nature tin move synchronized yesteryear applying a wrapper using synchronized Map. Here are simply about of the mutual differences betwixt ConcurrentHashMap in addition to synchronized map inwards Java

ConcurrentHashMap does non allow nothing keys or nothing values piece synchronized HashMap allows i nothing key.

Further Learning
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