An efficient (both memory and time) implementation of a Set used to verify that a given word is contained within the set. The general usage pattern is expected to be such that most checks are positive, ie. that the word indeed is contained in the set.

Performance of the set is comparable to that of java.util.TreeSet for Strings, ie. 2-3x slower than java.util.HashSet when using pre-constructed Strings. This is generally result of algorithmic complexity of structures; Word and Tree sets are roughly logarithmic to the whole data, whereas Hash set is linear to the length of key. However:

• WordSet can use char arrays as keys, without constructing Strings. In cases where there is no (need for) Strings, WordSet seems to be about twice as fast, even without considering additional GC caused by temporary String instances.
• WordSet is more compact in its memory presentation; if Strings are shared its size is comparable to optimally filled HashSet, and if no such Strings exists, its much more compact (relatively speaking)

Although this is an efficient set for specific set of usage patterns, one restriction is that the full set of words to include has to be known before constructing the set. Also, the size of the set is limited to total word content of about 20k characters; factory method does verify the limit and indicates if an instance can not be created.