Java hashmaps without the value?

java hashmap lookup containskey
jbu picture jbu · May 13, 2009 · Viewed 14.4k times · Source

Let's say I want to put words in a data structure and I want to have constant time lookups to see if the word is in this data structure. All I want to do is to see if the word exists. Would I use a HashMap (containsKey()) for this? HashMaps use key->value pairings, but in my case I don't have a value. Of course I could use null for the value, but even null takes space. It seems like there ought to be a better data structure for this application.

The collection could potentially be used by multiple threads, but since the objects contained by the collection would not change, I do not think I have a synchronization/concurrency requirement.

Can anyone help me out?

Answer

Dan Lew picture Dan Lew · May 13, 2009

Use HashSet instead. It's a hash implementation of Set, which is used primarily for exactly what you describe (an unordered set of items).

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