Which Data Structure should I use to store words from a novel?
You will probably end up using two nested data structures. I would use a hashmap with the words as keys. The value would be an array/list/set (depending on what you want to do with the occurrence data) containing an item for each occurrence of the word. The item would store whatever you needed (line number, etc). The number of occurrences would just be the size of this array/list/set.