A list is like a big long page full of names. But what if you also want, for each name, an
address? Or for every car in the garage list, you want details about that car? You need a
dictionary. A dictionary lets you take a special value—the key—and associate that key
with a bunch of data—the value. And one more thing: a specific key can only appear
once in any dictionary.
Dictionary <Tkey, TValue> kv = new Dictionary <TKey, TValue>()
Java uses Map or table(like HashTable) to deal with key/value case. Still, too many options's in Java World.