When would you choose a TreeMap or LinkedHashMap over a plain HashMap?

Use HashMap as the default for O(1) average access with no ordering guarantees.

Use LinkedHashMap when you need predictable iteration order — insertion order, or access order for building an LRU cache via removeEldestEntry. Use TreeMap when you need sorted keys or range queries (the NavigableMap operations: floorKey, ceilingKey, subMap, headMap), accepting O(log n) operations and a Comparable key or supplied Comparator. The choice is driven entirely by the ordering and navigation guarantees you need versus raw speed.