NOTE

Java Map Implementations Compared

Choosing HashMap, LinkedHashMap, TreeMap, ConcurrentHashMap, and synchronized/legacy maps.

JavaCreated 01/17/2020Updated 09/15/20261 min readhistorical

This is a historical learning note and may contain outdated or incomplete understanding.

HashMap: default mutable hash map; no ordering guarantee.
LinkedHashMap: deterministic insertion/access iteration order.
TreeMap: sorted/navigable map based on key ordering.
ConcurrentHashMap: concurrent shared access with atomic compound map operations.
synchronized wrappers / Hashtable: coarse-lock alternatives, usually not the first choice for scalable concurrency.

Choose based on ordering, concurrency, null policy, and operation needs rather than one “fastest map” rule.