Creating Dictionary in java?

Question

Everywhere on net, here is the way

Map<String, String> map = new HashMap<String, String>();
map.put("dog", "type of animal");
System.out.println(map.get("dog"));

My point is should it not be Treemap considering dictionary has to be sorted? Agreed lookup wont be optimized in case of Treemap but considering sorting its best data structure

UPDATE :- one more requirement is return the lexicographically nearest word if the word searched is not present . I am not sure how to achieve it?

Answer 1

If you need the map sorted by its keys, then use TreeMap, which "...provides guaranteed log(n) time cost for the containsKey, get, put and remove operations." If not, use the more general HashMap (which "...provides constant-time performance for the basic operations (get and put), assuming the hash function disperses the elements properly among the buckets..."), or one of the other Map implementations, depending on your need.

Answer 2

If you want to get value for given key and if the probability of having the exact match of key in hashmap is less then using hashmap wont give you benefit of direct lookup. If using TreeMap you can get list of keys which is already ordered and can perform a binary search on the list. While searching compare key lexicographically. Continue binary search till the lexicographic distance between two keys is minimum or 0.

Answer 3

Dictionary is no longer a term used in the language. You'll get multiple answers.

I know that Objective-C uses a class called Dictionary that is as a Key / Value data structure. The fact that it's named Dictionary leads me to believe that is the ordering of the objects, I imagine the Key has to be a string or char

So, it depends on the entire question.

When someone says they want to create a Key/Value data structure that is ordered alphabetically, or a "Dictionary", the answer is:

TreeMap<String, Object> map = new TreeMap<>()

If someone is asking how to create a Key/Value object similar to a Dictionary in whatever language, they will likely get any of the java.util classes that implement the Map<K, V> interface, for example HashMap, TreeMap. A good answer would be a TreeMap.

In this case telling someone to use a HashMap is not debatable, because the answer is as vague as the question.