Hash table (Hashtable)

A hash table (Hashtable) in the. NET framework, Hashtable is a container provided by the System.Collections namespace for handling and performing key-value pairs that resemble Key/value, Where key is usually used to quickly find, while key is case-sensitive; value is used to store values corresponding to key. Key/value key value pairs in Hashtable are of type object, so hashtable can support any type of Key/value key-value pairs. Second, the simple operation of a hash table adds a Key/value key value pair: Hashtableobject.add (Key,value); Removes a Key/value key value pair in a 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); The following console program will contain all of the above operations: using System; Using System.Collections; When using Hashtable, you must introduce this namespace class Hashtable {public static void Main () {hashtable ht=new hashtable ();///Create a Hashtable instance HT . Add ("E", "E");//Adds Key/value key value to HT. ADD ("A", "a"); Ht. ADD ("C", "C"); Ht. ADD ("B", "B"); String s= (String) ht["A"]; if (HT. Contains ("E"))//To determine whether a hash table contains a particular key, its return value is True or False Console.WriteLine ("The E key:exist"); Ht. Remove ("C");/Removes a Key/value key value pair Console.WriteLine (ht["A"]);//This outputs a HT. Clear ();/Remove all elements Console.WriteLine (ht["A"]); There will be no output}} Three, traversal hash table traversal hash table requires the use of DictionaryEntry Object, the code is as follows: for (DictionaryEntry de in HT)//ht is a Hashtable instance {Console.WriteLine (DE). Key);//de. Key corresponds to the Key/value key value pair key Console.WriteLine (DE. Value);//de. Key corresponds to the Key/value key value of four, sorting the hash table to sort the hash table here the definition is to rearrange the keys in the Key/value key value pairs by a certain rule, but in reality this definition is not possible. Because we can't rearrange keys directly in Hashtable, if you need Hashtable to provide some sort of rule output, you can use a workaround: ArrayList akeys=new ArrayList (ht. Keys); Don't forget to import the System.Collections Akeys. Sort (); Sort for alphabetically (string Skey in Akeys) {Console.Write (Skey + ":"); Console.WriteLine (Ht[skey]);//sorted after output}