NOTE
LinkedHashMap
Insertion/access-order HashMap with a linked iteration order and the basis of simple LRU-style maps.
This is a historical learning note and may contain outdated or incomplete understanding.
LinkedHashMap combines hash-based lookup with a linked ordering of entries.
It can maintain insertion order or access order. Access-order mode plus removeEldestEntry can implement a small simple LRU-style map, but this is not automatically a production cache: it lacks built-in concurrency, expiration, size-by-weight, loading, and observability features.
Iteration follows the maintained linked order. The collection itself is not thread-safe without external coordination.