Synchronized Collections vs Concurrent Collections

In this post, we will learn the difference between Synchronized Collections and Concurrent Collections in Java. This is a frequently asked question in Java interviews for beginners. Let's dive into it.

Difference between Synchronized Collections and Concurrent Collections in Java

Feature	Synchronized Collections	Concurrent Collections
Thread Safety	Thread-safe using locks	Thread-safe using non-blocking algorithms or fine-grained locking mechanisms
Locking Mechanism	Locks the entire collection	Utilizes non-blocking algorithms or fine-grained locks to allow concurrent access
Performance	May suffer from contention and performance issues in high-concurrency scenarios	Designed for high-concurrency scenarios with better performance in multi-threaded environments
Collection Types	Synchronized versions of standard collections (e.g., Collections.synchronizedList, Collections.synchronizedMap)	A separate set of classes in java.util.concurrent package (e.g., ConcurrentHashMap, ConcurrentSkipListMap)
Blocking Operations	Blocking operations when modifying the collection	Non-blocking operations for read and some write operations, providing better concurrency
Iterators	May throw ConcurrentModificationException during iteration if the collection is modified	Designed to handle concurrent modifications gracefully and not throw ConcurrentModificationException