Prev Next

Java / Concurrent collections

Difference between synchronizedMap and ConcurrentHashMap in Java.

The synchronizedMap(HashMap) locks the entire map while ConcurrentHashMap synchronizes or locks on the certain portion of the Map . To optimize the performance of ConcurrentHashMap , Map is divided into different Segments.

ConcurrentHashMap shows good performance than synchronized version of HashMap.

When you read from a ConcurrentHashMap using get(), there are no locks, contrary to the Synchronized HashMap for which all operations are simply synchronized.

ConcurrentHashMap can guarantee that there is no ConcurrentModificationException thrown while one thread is updating the map and another thread is traversing the iterator obtained from the map. However, Collections.synchronizedMap() is not guaranteed on this.

ConcurrentHashMap will not preserve the order of elements in the Map passed in. It is similar to HashMap when storing data. There is no guarantee that the element order is preserved. While Collections.synchronizedMap() will preserve the elements order of the Map passed in.

Invest now in Acorns!!! 🚀 Join Acorns and get your $5 bonus!

Invest now in Acorns!!! 🚀
Join Acorns and get your $5 bonus!

Earn passively and while sleeping

Acorns is a micro-investing app that automatically invests your "spare change" from daily purchases into diversified, expert-built portfolios of ETFs. It is designed for beginners, allowing you to start investing with as little as $5. The service automates saving and investing. Disclosure: I may receive a referral bonus.

Invest now!!! Get Free equity stock (US, UK only)!

Use Robinhood app to invest in stocks. It is safe and secure. Use the Referral link to claim your free stock when you sign up!.

The Robinhood app makes it easy to trade stocks, crypto and more.

Webull! Receive free stock by signing up using the link: Webull signup.

More Related questions...

Explain concurrent collection API. List some of the concurrency collection interfaces. Explain BlockingQueue in Java concurrent collections. I have one List of Map like - List> list = new ArrayList>(); I want to return the Key if any value passed by user is equal to the value present in Map using Java 8 . One way to doing is - Map data = new HashMap<>(); list.stream().forEach(map -> { data.putAll(map.entrySet().stream() .collect(Collectors.toMap(entry -> entry.getKey(), entry -> (String) entry.getValue()))); }); String result = data.entrySet().stream() .filter(map -> "def".equals(map.getValue())) .map(map -> map.getKey()) .collect(Collectors.joining()); But I want to do to it without using collect(). Please help me on that. Thank you. What are the 4 forms of BlockingQueue methods? Does BlockingQueue supports removal of arbitrary element? Is BlockingQueue implementations are thread safe? Define poison pill or object in Java collections. What does drainDo method in BlockingQueue do? List the implementations of BlockingQueue. Does BlockingQueue allow null elements? Explain ArrayBlockingQueue in Java concurrency collections. What is Bounded buffer? Explain DelayQueue in Java Concurrent collections. Explain LinkedBlockingQueue in Java concurrent collections. Explain PriorityBlockingQueue in Java concurrency collections. Difference between ArrayBlockingQueue and LinkedBlockingQueue. Difference between synchronizedMap and ConcurrentHashMap in Java. Why does ConcurrentHashMap does not allow null key or values? Can we use ConcurrentHashMap in a single threaded application? Difference between Hashtable and ConcurrentHashMap in Java. What is High throughput computing? Difference between ConcurrentHashMap and HashMap. Explain SynchronousQueue in Java concurrent collections. What is shutdown hook in Java Thread? Difference between Runnable and Callable in Java Thread. How to stop a running thread in Java? Why is Thread.stop deprecated? Why are Thread.suspend and Thread.resume deprecated? Difference between findMonitorDeadlockedThreads and findDeadlockedThreads in Java ThreadMXBean. Define ownable synchronizer in Java thread. Explain ThreadMXBean in Java. Design patterns used in Java multithreading. Is final field initialized in constructor thread-safe? Difference between submit and execute method with ThreadPoolExecutor. If a synchronized method calls another non-synchronized method, is there a lock on the non-synchronized method? What is defensive copying in Java? What is Program counter? What is Java Shutdown Hook? When to use FixedThreadPool in Java? Advantages of immutable objects in multithreaded environment. Difference between LinkedBlockingQueue and ConcurrentLinkedQueue in Java. How to make sure the overrided method is also synchronized in Java? Explain ConcurrentHashMap in Java. Is ConcurrentHashMap thread-safe in Java? Can multiple threads read from ConcurrentHashMap at same time? How ConcurrentHashMap works internally? How does ConcurrentHashMap achieve thread-safety? How to atomically update a value in ConcurrentHashMap? Is Iterator of ConcurrentHashMap fail-safe or fail-fast? What is Spliterator in Java 8? What is reactive streaming in Java9? Why reactive programming is preferred? Explain stream pipelining in Java 8. How does CopyOnWriteArrayList internally works in Java? Difference between ConcurrentSkipListMap and ConcurrentHashMap.
Show more question and Answers...

Java Serialization

Comments & Discussions

Interviews Questions

About Javapedia.net

Javapedia.net is for Java and J2EE developers, technologist and college students who prepare of interview. Also this site includes many practical examples.

This site is developed using J2EE technologies by Steve Antony, a senior Developer/lead at one of the logistics based company.

contact: javatutorials2016[at]gmail[dot]com

Kindly consider donating for maintaining this website. Thanks.

Copyright © 2026, javapedia.net, all rights reserved. privacy policy.

DMCA.com Protection Status