Java - Is it common practice to use a hashtable (eg HashMap) to map objects to themselves?

Question

I'm making a java application that is going to be storing a bunch of random words (which can be added to or deleted from the application at any time). I want fast lookups to see whether a given word is in the dictionary or not. What would be the best java data structure to use for this? As of now, I was thinking about using a hashMap, and using the same word as both a value and the key for that value. Is this common practice? Using the same string for both the key and value in a (key,value) pair seems weird to me so I wanted to make sure that there wasn't some better idea that I was overlooking.

I was also thinking about alternatively using a treeMap to keep the words sorted, giving me an O(lgn) lookup time, but the hashMap should give an expected O(1) lookup time as I understand it, so I figured that would be better.

So basically I just want to make sure the hashMap idea with the strings doubling as both key and value in each (key,value) pair would be a good decision. Thanks.

Answer 1

I want fast lookups to see whether a given word is in the dictionary or not. What would be the best java data structure to use for this?

This is the textbook usecase of a Set. You can use a HashSet. The naive implementation for Set<T> uses a corresponding Map<T, Object> to simply mark whether the entry exists or not.

Answer 2

If you're storing it as a collection of words in a dictionary, I'd suggest taking a look at Tries. They require less memory than a Set and have quick lookup times of worst case O(string length).