Sunday, 3 May 2015

How to use C# HashTable Class ?

You already have a System.Collections.Generic namespace, but a Hastable is not part of this collection - it's part of the normal Collections namespace.

Hashtable in C# represents a collection of key/value pairs which maps keys to value. Any non-null object can be used as a key but a value can. We can retrieve items from hashTable to provide the key . Both keys and values are Objects.

// Creating an object of HashTable
  Hashtable ht = new  Hashtable();


Operation on HashTable


   1.   Add:   Its use to add a pair of value in HashTable
      Syntex-         ht.Add(keyObj, valueObj)
      Example-      ht.Add(1, Monday)

   2.  ContainsKey:   Check if a specified key exist or not and retruns boolean value
          Syntex-             ht.ContainsKey(keyObj)
          Example-          bool  IsExist  =    ht.ContainsKey(1))
      Return value-  True

  3.  ContainsValue:   Check if a specified Value exist or not and retruns boolean value
          Syntex-             ht.ContainsValue(valueObj)
          Example-          bool  IsExist  =    ht.ContainsValue(Monday))
      Return value-  True
  
   4.  Remove:  Remove the specified Key and corresponding Value if exist
          Syntex -       ht.Remove(keyObj);
          Example-     ht.Remove(1);

 Source Code Example:-

         In below example I explained each above operation 


using System;
using System.Linq;
using System.Text;
using System.Globalization;
using System.Collections;

Namespace ConsoleDemoApp
{
    Class Test
    {
        /* program to implement Dictionay in c# */

        public static void Main(string[] args)
        {
            int inputNum=0;

          
            Console.Write("\nEnter number of day in a Week: ");
            inputNum= int.Parse(Console.ReadLine());

            HashTableExample ht = new HashTableExample();
            ht.HT_Operations(inputNum);
            Console.ReadKey();
        }
    }

  
  

    //
    Public class HashTableExample
    {
        Public void HT_Operations(int inputNum)
        {
            string dayName;
           
           Hashtable WeekDays = new  Hashtable();
           for(int i=0; i<inputNum; i++)
            {
                Console.Write("\nEnter {0} day of Week: ", i+1);
                dayName = Console.ReadLine();
                 WeekDays.Add(i,dayName);
                 Console.Write("\n");
            }

            // print all
            Console.Write("\nEntered Days are: \n");
            foreach(DictionaryEntry day in WeekDays)
            {
               Console.Write(day.Value);
               Console.Write("\n");
            }

            //print a single day 
            Console.Write(WeekDays[3].ToString());
            Console.Write("\n");


            //Search an Item by value
            Console.Write("\nEntered a Days for search: \n");
            dayName = Console.ReadLine();
            if (WeekDays.ContainsValue(dayName))
            {
                Console.Write("\n {0} is Found in the Dictionay: \n", dayName);
            }
            else
            {
                Console.Write("Not Found!");
            }


            //Search an Item by key
            Console.Write("\nEntered a key for search: \n");
           int key = int.Parse(Console.ReadLine());
           if (WeekDays.ContainsKey(key))
            {
                Console.Write("\nFor entered key {0} the day name is: {1} \n", key, WeekDays[key].ToString());
            }
            else
            {
                Console.Write("Not Found!");
            }

           //now remove an Item using key
            Console.Write("\nEntered a key to remove a Day: \n");
            key = int.Parse(Console.ReadLine());
            if (WeekDays.ContainsKey(key))
            {
                Console.Write("\nThe Day {0} has been removed: \n", WeekDays[key].ToString());
                WeekDays.Remove(key);
            }
            else
            {
                Console.Write("No Day exits at key:  {0}", key);
            }


            // print the remaining days
            Console.Write("\nRemaing Days are: \n");
            foreach(DictionaryEntry day in WeekDays)
            {
                Console.Write(day.Key + " - " + day.Value);
                Console.Write("\n");
            }
        }
    }
}


In above program I entered number of day in week is 7. After it will ask enter all day one by one 
and after that it will print instructions and ask relevant key/value to enter

Output:-
















No comments:

Post a Comment