Which methods of hashtable is synchronized

Furthermore, the synchronized wrapper ensures that there is only one writer writing at a time. Enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

The following code example shows how to lock the collection using the SyncRoot during the entire enumeration:. Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services. Privacy policy. We can also increase or decrease the default concurrency level while creating ConcurrentHashMap by using below constructor :. Thread acquires a lock on segment in put operation and at a time only one thread can write in that segment.

Thread doesn't acquire a lock on segment in get operation and any number of threads can read from the same segment. If one thread is writing in a segment, can another thread read from that segment? ConcurrentHashMap doesn't allow null keys and null values. We will soon publish our article on the internal working of ConcurrentHashMap.

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Posted by Abhi Andhariya. In all core java interviews, you will definitely face questions on HashMap Internals like, what is the use of hashCode and equals method? How put and get method works in HashMap? Hashtable Hashtable is a legacy class available since jdk 1. SynchronizedMap SynchronizedMap is a static inner class of utility class java.

For Example, import java. ConcurrentHashMap Hashtable and SynchronizedMap both acquires lock on entire Map object which provides thread-safety, but not good performance as at a time only one thread can access that Map instance. We can also increase or decrease the default concurrency level while creating ConcurrentHashMap by using below constructor : ConcurrentHashMap int initialCapacity, float loadFactor, int concurrencyLevel Can Multiple thread write in the same segment?

Can two threads write in the different segment? Two threads are allowed to write concurrently in different segments. Can Multiple thread read from the same segment?

If you want high level of data consistency, then only consider using synchronized HashMap. Otherwise, in all the concurrently executing multi threaded circumstances, ConcurrentHashMap is the best choice. Your email address will not be published. Notify me of follow-up comments by email. Notify me of new posts by email. Skip to content. MainMenu MainMenu. Leave a Reply Cancel reply Your email address will not be published.

By default, 16 threads can perform update operations and any number of threads can perform read operations at a time.

Allows one null key and any number of null values. Use only when high level of data consistency is required in multi threaded environment. Not recommended as it is a legacy class.