hashtable

I am trying to figure out when and why to use a Dictionary or a HashTable. I have done a bit of a search on here and have found people talking about the generic advantages of the Dictionary which I totally agree with, which leads the boxing and unboxing advantage for a slight performance gain. But I have also read the Dictionary will not always return the objects in the order they are inserted, thing it is sorted. Where as a HashTable will. As I understand it this leads to the HashTable being far faster for some situations. My question is really, what might those situations be? Am I just wrong

I've heard in my degree classes that a HashTable will place a new entry into the 'next available' bucket if the new Key entry collides with another. How would the HashTable still return the correct Value if this collision occurs when calling for one back with the collision key? I'm assuming that the Keys are String type and the hashCode() returns the default generated by say Java. If I implement my own hashing function and use it as part of a look-up table (i.e. a HashMap or Dictionary ), what strategies exist for dealing with collisions? I've even seen notes relating to prime numbers!

This question already has an answer here: Two way/reverse map 13 answers Python dict is a very useful data-structure: d = {'a': 1, 'b': 2} d['a'] # get 1 Sometimes you'd also like to index by values. d[1] # get 'a' Which is the most efficient way to implement this data-structure? Any official recommend way to do it? Here is a class for a bidirectional dict , inspired by Finding key from value in Python dictionary and modified to allow the following 2) and 3). Note that : 1) The inverse directory bd.inverse auto-updates itself when the standard dict bd is modified. 2) The inverse directory bd