HashSet hastable Dictionary concurrentdictionary Difference

1.HashTable

A hash table (HashTable) represents a collection of key/value pairs. In the. NET Framework, Hashtable is a container provided by the System.Collections namespace that handles and behaves like Key-value key-value pairs, where key is usually used for quick lookups, and key is case-sensitive; value is used to store the value corresponding to key. Key-value Key-value pairs in Hashtable are all object types, so hashtable can support any type of KeyValue key-value pair, and any non-null object can be used as a key or a value.

Add a key/key value pair to the hash table: Hashtableobject.add (key,);

Remove a key/key value pair in the hash table: Hashtableobject.remove (key);

Remove all elements from the hash table: Hashtableobject.clear ();

Determines whether a hash table contains a specific key key:HashtableObject.Contains (key);

　　2.HashSet

The Hashset<t> class is designed to perform high-performance set operations such as intersection, set, and difference set for two sets. The collection contains a set of elements that do not recur and have no attribute order, and HashSet refuses to accept duplicate objects.

Some of the features of hashset<t> are as follows:

A. The values in hashset<t> cannot be duplicated and have no order.

B. The capacity of the hashset<t> is automatically added as needed.

　　3.Dictionary

Dictionary represents a collection of keys and values.

Dictionary<string, string> is a generic

He has a set of functions that can sometimes be seen as an array.

His structure is this: Dictionary<[key], [value]>

His feature is that the deposit object is required to be stored with the [key] value one by one in the generic

To find the corresponding value by a certain [key]

　　The difference between 4.HashTable and dictionary:

(1). Hashtable does not support generics, while dictionary supports generics.

(2). The Hashtable element is of type Object, so boxing and unpacking is usually the case when storing or retrieving a value type, so you may need to do some type conversion, and it can be time-consuming to int,float these value types for boxing.

(3). Dictionary is recommended in single-threaded programs, with a generic advantage, with faster read speeds and fuller capacity utilization. Hashtable is recommended in multithreaded programs, the default Hashtable allows single-threaded writes, multithreaded reads, and further calls to the Hashtable Synchronized () method to obtain a fully thread-safe type. While Dictionary is non-thread-safe, it must be protected by the use of the lock statement, and the efficiency is greatly reduced.

Concurrentdictionary Concurrentqueue concurrentstack Series is a thread-safe generic collection of. NET4.0, which is a thread-safe improved version of queue, Stack, and dictionary.

usingSystem;usingSystem.Diagnostics;usingSystem.Text;usingSystem.Collections;usingSystem.Collections.Generic;classtest{//both Hashtable and dictionary use hashing algorithms//The latter is generic and does not have a common packing-unboxing operation for the former//The latter is non-thread-safe, formerly thread-safe, and concurrentdirctionary is thread-safe//The latter parameter is a generic type and is flexible and type safe: The former is of type object, type is unsafe//    Static voidMain (string[] args) {Hashtable HT=NewHashtable (); Ht. ADD (1,1); ht[1] =1;//foreach (Keyvaluepair<object, object> p in HT)//This is not accessible because Hashtable is not generic and throws an exception//         {//Console.WriteLine (P.key + "," + p.value);//         }dictionary<int,int> dict =Newdictionary<int,int>(); Dict. ADD (1,1); dict[2] =2;//Normal        intx = dict[3] =3;//Normal//int y = dict[4];//Exception        foreach(keyvaluepair<int,int> Pinchdict) {Console.WriteLine (P.key+","+p.value); }        intXT; Dict. TryGetValue (5, outXT);//This is more efficient than judging containskey (5) and then dict[5], eliminating many of the traversalConsole.WriteLine (XT); }}

HashSet hastable Dictionary concurrentdictionary Difference