Brief introduction and application of. Net hashtable

Hashtable
1. Brief description of the hash table (hashtable)

In. in net work, hashtable is system. A container provided by the collections namespace is used to process and present key-value pairs similar to key/. The key is usually used for quick search, and the key is case sensitive; store the value corresponding to the key. In hashtable, key/key-value pairs are of the object type, so hashtable can support any type of key/key-value pairs.

Ii. Simple operations on Hash Tables

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 ();
Determine whether the hash table contains the specified key: hashtableobject. Contains (key );

The following console contains all the preceding operations:
Using system;
Using system. collections; // This namespace must be introduced when hashtable is used.

Class hashtable {public static void main () {hashtable ht = new hashtable (); // create a hashtable instance ht. add ("e", "E"); // Add key/key value pair ht. add ("A", "A"); ht. add ("C", "C"); ht. add ("B", "B"); string S = (string) HT ["A"]; // obtain the value if (HT. contains ("e") // determines whether the hash table contains a specific key. The return value is true or false console. writeline ("the e key: exist"); ht. remove ("C"); // remove a key/key-value pair from the console. writeline (HT ["A"]); // output a HT here. clear (); // remove all elements from the console. writeline (HT ["A"]); // there will be no output here }}

3. traverse the hash table

Dictionaryentry object is required to traverse a hash table. The Code is as follows:

For (dictionaryentry de in HT) // HT is a hashtable instance {console. writeline (de. key); // de. the key corresponds to the key/key-Value Pair key console. writeline (De .); // de. key corresponds to key/key-Value Pair}

4. Sort hash tables

The definition of sorting hash tables here is to re-arrange the keys in key/key-value pairs according to certain rules, but in fact this definition cannot be implemented, because we cannot re-arrange keys directly in hashtable, if hashtable needs to provide output of certain rules, we can adopt a work und:

Arraylist akeys = new arraylist (HT. keys); // do not forget to import system. collections // This improves the query speed. sort (); // sort in alphabetical order for (string skey in akeys) {console. write (skey ":"); console. writeline (HT [skey]); // output after sorting}

5. access other objects in the hash table
// Class Object

Public class person {private string firstname; private string lastname; Public Person (string first, string last) {firstname = first; lastname = last ;} public String fullname {get {return firstname + "" + lastname ;}}// the access process protected void page_load (Object sender, eventargs E) {person Scott = new person ("Scott", "hanselman"); person bill = new person ("bill", "evjen "); person srini = new person ("Srinivasa", "sivakumar"); hashtable peoplehashtable = new hashtable (); peoplehashtable. add ("sh", Scott); peoplehashtable. add ("be", Bill); peoplehashtable. add ("SS", srini); person found = (person) lelehashtable ["sh"]; response. write (found. fullname + "<br/>"); found = (person) lelehashtable ["be"]; response. write (found. fullname + "<br/>"); found = (person) lelehashtable ["sh"]; response. write (found. fullname + "<br/>"); // write Method 1: // foreach (dictionaryentry de in lelehashtable) // {// response. write (de. key. tostring () + ":" + (person) de. value ). fullname + // "<br/>"); //} // write Method 2: // foreach (string s in peoplehashtable. keys) // {// response. write (S + "<br/>"); // foreach (person P in peoplehashtable. values) // {// response. write (P. fullname + "<br/> ");//}}

6. How to read the key based on value in hashtable

Hashtable t = new Hashtable();foreach( DictionaryEntry i in t ){if(  i.Value == "value1" ) return i.Key ;}