AccessOrder

AccessOrder refers to a property in some map-like data structures that controls the order in which elements are iterated based on how recently they were accessed, rather than the order in which they were inserted. In an access-ordered structure, each read or write can move an entry to reflect its recent use, resulting in an ordering from least-recently accessed to most-recently accessed.

In Java, LinkedHashMap supports an accessOrder mode through a constructor parameter. The form LinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder) creates a map that, when accessOrder is true, maintains its entries in access order. With this mode, calling get or put updates the position of the involved entry so that recently accessed items are placed toward the end. If the map is configured to evict entries, the eldest entry (the one at the beginning) is removed first, enabling simple least-recently-used (LRU) caching behavior. This is commonly achieved by subclassing LinkedHashMap and overriding removeEldestEntry to specify a maximum size.

Implementation details include that LinkedHashMap uses a doubly linked list to track order and that access-order updates are O(1) for typical operations. It is not synchronized by default, so concurrent use requires external synchronization or a concurrent alternative.

Access-order structures are widely used for cache design and other scenarios where recent activity should influence iteration order. Related concepts include eviction policies, LRU caches, and insertion-order configurations in similar data structures.