CODEWITHSUNDEEP
javalinkedhashmap
Diego
Diego

Reputation: 17140

Does entrySet() in a LinkedHashMap also guarantee order?

I am using a linkedHashMap to guarantee order when someone tries to access it. However, when it comes time to iterate over it, does using entrySet() to return key/value pairs guarantee order as well? No changes will be made while iterating.

EDIT: Also, are there any adverse effects from iterating through the map by iterating through its keys and calling get?

Upvotes: 90

Views: 38416

Answers (3)

Michael Myers
Michael Myers

Reputation: 191945

According to the Javadocs, yes.

This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order).

As for the edit, no, it should work just fine. But the entry set is somewhat faster since it avoids the overhead of looking up every key in the map during iteration.

Upvotes: 58

Daniel F. Thornton
Daniel F. Thornton

Reputation: 3685

If you're sure no changes will be made during the iteration, then proper ordering with entrySet() is guaranteed, as stated in the API.

Upvotes: 2

Robert
Robert

Reputation: 8609

This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order). Note that insertion order is not affected if a key is re-inserted into the map. (A key k is reinserted into a map m if m.put(k, v) is invoked when m.containsKey(k) would return true immediately prior to the invocation.)

Upvotes: 1

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