1. Brief description of the hash table (hashtable)
In the. NET Framework, hashtable is a container provided by the system. Collections namespace.Key/valueKey-value pairs. The key is usually used for quick search, and the key is case sensitive. The value is used to store the value corresponding to the key. In hashtable, key/value pairs are of the object type, so hashtable can support any type of key/value pairs.
Ii. Simple operations on Hash Tables
Add a key/value Key-value pair to the hash table: hashtableobject.Add (Key, value);
Remove a key/value pair in the hash table: hashtableobject.Remove (key);
Remove all elements from the hash table: hashtableobject.Clear ();
Checks whether the hash table contains a specific 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/value pairs
Ht. Add ("A", "");
Ht. Add ("C", "C ");
Ht. Add ("B", "B ");
String S = (string) HT ["A"];
If (HT. Contains ("e") // checks 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/value pair
Console. writeline (HT ["A"]); // output
Ht. Clear (); // remove all elements
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:
Foreach (dictionaryentry de in HT) // HT is a hashtable instance.
{
Console. writeline (De. Key); // de. Key corresponds to the key-Value Pair
Console. writeline (De. Value); // de. Key corresponds to the key/value Key-Value Pair Value
}
4. Sort hash tables
The definition of sorting hash tables here is to re-arrange the keys in 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
Akeys. Sort (); // sort by letter
For (string skey in akeys)
{
Console. Write (skey + ":");
Console. writeline (HT [skey]); // output after sorting