Quick Answer: What is difference between Hashtable and ConcurrentHashMap in Java?

Hashtable is belongs to the Collection framework; ConcurrentHashMap belongs to the Executor framework. Hashtable uses single lock for whole data. ConcurrentHashMap uses multiple locks on segment level (16 by default) instead of object level i.e. whole Map . ConcurrentHashMap locking is applied only for updates.

What is ConcurrentHashMap and Hashtable in Java Why is ConcurrentHashMap considered faster than Hashtable?

Answer: ConcurrentHashMap is introduced in Java 1.5. ConcurrentHashMap uses multiple buckets to store data. This avoids read locks and greatly improves performance over a HashTable.

What is the difference between HashMap and ConcurrentHashMap?

HashMap is a powerful data structure in Java used to store the key-pair values. The ConcurrentHashMap is a synchronized collection class. … The HashMap is non-thread-safe and can not be used in a Concurrent multi-threaded environment.

Can we replace Hashtable with ConcurrentHashMap?

5 release to replace legacy class Hashtable. In multithreaded environment ConcurrentHashMap performs better as compared to Hashtable and Synchronized Map as well. … As ConcurrentHashMap is introduced to replace Hashtable, it become obvious to ask questions around HashMap and ConcurrentHashMap in interviews.

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Is ConcurrentHashMap slower than HashMap?

Only modifying operations on ConcurrentHashMap are synchronized. Hence, add or remove operations on ConcurrentHashMap are slower than on HashMap . The read operations on both, ConcurrentHashMap and HashMap , give same performance as read operations on both maps are not synchronized.

What is difference between synchronizedMap and ConcurrentHashMap?

synchronizedMap() requires each thread to acquire a lock on the entire object for both read/write operations. By comparison, the ConcurrentHashMap allows threads to acquire locks on separate segments of the collection, and make modifications at the same time.

What is a Hashtable in Java?

Hashtable was part of the original java. util and is a concrete implementation of a Dictionary. … Like HashMap, Hashtable stores key/value pairs in a hash table. When using a Hashtable, you specify an object that is used as a key, and the value that you want linked to that key.

What is difference between HashMap and Hashtable?

HashMap is non-synchronized. It is not thread-safe and can’t be shared between many threads without proper synchronization code whereas Hashtable is synchronized. … HashMap allows one null key and multiple null values whereas Hashtable doesn’t allow any null key or value.

What is the difference between HashMap and ConcurrentHashMap follow up with what is the difference between CHM and synchronized map?

ConcurrentHashMap allows performing concurrent read and write operation. Hence, performance is relatively better than the Synchronized Map. In Synchronized HashMap, multiple threads can not access the map concurrently. Hence, the performance is relatively less than the ConcurrentHashMap.

What is the use of ConcurrentHashMap in Java?

ConcurrentHashMap: It allows concurrent access to the map. Part of the map called Segment (internal data structure) is only getting locked while adding or updating the map. So ConcurrentHashMap allows concurrent threads to read the value without locking at all. This data structure was introduced to improve performance.

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Why ConcurrentHashMap is fail-safe?

This is because, they operate on the clone of the collection, not on the original collection and that’s why they are called fail-safe iterators. Iterator on CopyOnWriteArrayList, ConcurrentHashMap classes are examples of fail-safe Iterator.

Why do we need ConcurrentHashMap?

You should use ConcurrentHashMap when you need very high concurrency in your project. It is thread safe without synchronizing the whole map . Reads can happen very fast while write is done with a lock. There is no locking at the object level.

What is CopyOnWriteArrayList in Java?

CopyOnWriteArrayList is a thread-safe variant of ArrayList where operations which can change the ArrayList (add, update, set methods) creates a clone of the underlying array. CopyOnWriteArrayList is to be used in a Thread based environment where read operations are very frequent and update operations are rare.

What is difference between synchronized and concurrent collections in Java?

Answer. The main reason for this slowness is locking; synchronized collections lock the whole collection e.g. whole Map or List while concurrent collection never locks the whole Map or List. …

What is difference between wait and sleep in Java?

It tells the calling thread (a.k.a Current Thread) to wait until another thread invoke’s the notify() or notifyAll() method for this object, The thread waits until it reobtains the ownership of the monitor and Resume’s Execution.

Difference between wait and sleep in Java.

Wait() Sleep()
Wait() is not a static method. Sleep() is a static method.

Is map thread-safe Java?

Maps are naturally one of the most widely style of Java collection. And, importantly, HashMap is not a thread-safe implementation, while Hashtable does provide thread-safety by synchronizing operations. Even though Hashtable is thread safe, it is not very efficient. Another fully synchronized Map, Collections.

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