LinkedHashSet => Performance is likely to be just slightly below that of HashSet, due to the added eXPense of maintaining the linked list, with one exception: Iteration over a LinkedHashSet requires time PRoportional to the size of the set, regardless of its capacity. Iteration over a HashSet is likely to be more expensive, requiring time proportional to its capacity.
LinkedHashMap => Performance is likely to be just slightly below that of HashMap, due to the added expense of maintaining the linked list, with one exception: Iteration over the collection-views of a LinkedHashMap requires time proportional to the size of the map, regardless of its capacity. Iteration over a HashMap is likely to be more expensive, requiring time proportional to its capacity.
IdentityHashMap => This has better locality for large tables than does using separate arrays.) For many JRE implementations and Operation mixes, this class will yield better performance than HashMap (which uses chaining rather than linear-probing
