One more difference that I can find at the implementation of both the classes is as follows: • The Hashtable class has all its methods synchronized i.e. the locking is done at the method level and hence one can say that the mutex is always at the Hashtable object (this) level. • The method Collections.synchronizedMap(Map) … Read more
The answers so far have helped to define hash tables and explain some theory, but I think an example may help you get a better feeling for them. What is the difference between a hash table and just a normal array? A hash table and an array are both structures that allow you to store … Read more
var hash = {} hash[key] = value Object.keys(hash).forEach(function (key) { var value = hash[key] // iteration code })
If you’re using C++11, you have access to the <unordered_map> and <unordered_set> headers. These provide classes std::unordered_map and std::unordered_set. If you’re using C++03 with TR1, you have access to the classes std::tr1::unordered_map and std::tr1::unordered_set, using the same headers (unless you’re using GCC, in which case the headers are <tr1/unordered_map> and <tr1/unordered_set> instead). In all cases, … Read more
Because final marks the reference, not the object. You can’t make that reference point to a different hash table. But you can do anything to that object, including adding and removing things. Your example of an int is a primitive type, not a reference. Final means you cannot change the value of the variable. So, … Read more
Under the appropriate assumptions on the hash function being used, we can say that hash table lookups take expected O(1) time (assuming you’re using a standard hashing scheme like linear probing or chained hashing). This means that on average, the amount of work that a hash table does to perform a lookup is at most … Read more
1: What are the major differences, if any? Data.Map.Map is a balanced binary tree internally, so its time complexity for lookups is O(log n). I believe it’s a “persistent” data structure, meaning it’s implemented such that mutative operations yield a new copy with only the relevant parts of the structure updated. Data.HashMap.Map is a Data.IntMap.IntMap … Read more
First you shoud maybe read this article. When you use lists and you are looking for a special item you normally have to iterate over the complete list. This is very expensive when you have large lists. A hashtable can be a lot faster, under best circumstances you will get the item you are looking … Read more
java.util.HashMap is unordered; you can’t and shouldn’t assume anything beyond that. This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time. java.util.LinkedHashMap uses insertion-order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all … Read more
Wikipedia’s article on hash tables gives a distinctly better explanation and overview of different hash table schemes that people have used than I’m able to off the top of my head. In fact you’re probably better off reading that article than asking the question here. 🙂 That said… A chained hash table indexes into an … Read more