Java LinkedHashMap get first or last entry

java dictionary linkedhashmap
maiky picture maiky · Dec 20, 2009 · Viewed 129k times · Source

I have used LinkedHashMap because it is important the order in which keys entered in the map.

But now I want to get the value of key in the first place (the first entered entry) or the last.

Should there be a method like first() and last() or something like that?

Do I need to have an iterator to just get the first key entry? That is why I used LinkedHashMap!

Thanks!

Answer

skaffman picture skaffman · Dec 20, 2009

The semantics of LinkedHashMap are still those of a Map, rather than that of a LinkedList. It retains insertion order, yes, but that's an implementation detail, rather than an aspect of its interface.

The quickest way to get the "first" entry is still entrySet().iterator().next(). Getting the "last" entry is possible, but will entail iterating over the whole entry set by calling .next() until you reach the last. while (iterator.hasNext()) { lastElement = iterator.next() }

edit: However, if you're willing to go beyond the JavaSE API, Apache Commons Collections has its own LinkedMap implementation, which has methods like firstKey and lastKey, which do what you're looking for. The interface is considerably richer.

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