ConcurrentHashMap vs Synchronized HashMap in Java
Introduction In multi-threaded Java applications, managing shared data safely and efficiently is crucial. Two common approaches are using Synchronized HashMap (via Collections.synchronizedMap(...) ) and ConcurrentHashMap . While both aim to provide thread-safety, their implementations and performance characteristics differ significantly. This post explores these differences in detail. What is a Synchronized HashMap? Created by wrapping a regular HashMap using: Map<K, V> syncMap = Collections.synchronizedMap(new HashMap<>()); Enforces synchronization at the object level , meaning only one thread can access the map at any time (read or write). Supports null keys and values since it relies on HashMap behavior. Iterators are fail-fast , throwing ConcurrentModificationException if the map is modified while iterating. Simpler implementation, suitable when concurrency is low or performance is not cri...