Hash Table and Dictionary in C#

Question

Hi all, What is the difference between hash table and dictionary in C#?

Abhishek Jaiswal · Answer

heyy! check this http://www.c-sharpcorner.com/UploadFile/2072a9/dictionaries-and-hash-table-in-C-Sharp496/ :)

winston Gelmer · Answer

Hashtable and Dictionary are collection of data structures to hold data as key-value pairs. Dictionary is generic type, hash table is not a generic type. The Hashtable is a weakly typed data structure, so you can add keys and values of any Object Type to the Hashtable. The Dictionary class is a strongly types and you must specify the data types for both the key and value. Declaration: Hashtable numbers = new Hashtable(); Dictionary dictionary = new Dictionary (); More about... http://net-informations.com/faq/general/dictionary.htm http://csharp.net-informations.com/collection/dictionary.htm Winston

Satyapriya Nayak · Answer

Hashtable is also collection which takes a key corresponding to each values. If you want to find something in a hashtable you dont have to go through each value in hashtable, instead search for key values and is faster. Program that uses Hashtable [C#] using System; using System.Collections; class Program { static void Main() { Hashtable hashtable = new Hashtable (); hashtable[1] = "One"; hashtable[2] = "Two"; hashtable[13] = "Thirteen"; foreach (DictionaryEntry entry in hashtable) { Console.WriteLine("{0}, {1}", entry.Key, entry.Value); } } } Dictionary A Dictionary class represents a dictionary in C# that is used to represent a collection of keys and values pair of data. This article demonstrates how to use a dictionary in C#. The Dictionary class is a generic class and can store any data types. This class is defined in the System.Collections.Generic namespace. Before you use a Dictionary class in your code, you must import the System.Collections.Generic namespace using the following line. C# using System.Collections.Generic; VB.NET Imports System.Collections.Generic As other collection classes, the Dictionary class has Add, Remove, RemoveAt and other collection methods. The Key and Value property are used to extract a key and a value from an item in a Dictionary. The following code snippet creates a Dictionary, adds some data to it and reads data back. VB.NET Code: Imports System.Collections.Generic Module Module1 Sub Main() Dim AuthorList As New Dictionary ( Of String , Int16 ) AuthorList.Add( "Mahesh Chand" , 35) AuthorList.Add( "Mike Gold" , 25) AuthorList.Add( "Praveen Kumar" , 29) AuthorList.Add( "Raj Beniwal" , 21) AuthorList.Add( "Dinesh Beniwal" , 84) ' Read all data Console .WriteLine( "Authors List" ) For Each author As KeyValuePair ( Of String , Int16 ) In AuthorList Console .WriteLine( "Key = {0}, Value = {1}" , _ author.Key, author.Value) Next author Console .ReadKey() End Sub End Module C# Code: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Collections.Generic; namespace DictionarySample { class Program { static void Main( string [] args) { Dictionary string , Int16 > AuthorList = new Dictionary string , Int16 >(); AuthorList.Add( "Mahesh Chand" , 35); AuthorList.Add( "Mike Gold" , 25); AuthorList.Add( "Praveen Kumar" , 29); AuthorList.Add( "Raj Beniwal" , 21); AuthorList.Add( "Dinesh Beniwal" , 84); // Read all data Console .WriteLine( "Authors List" ); foreach ( KeyValuePair string , Int16 > author in AuthorList ) { Console .WriteLine( "Key = {0}, Value = {1}" , author.Key, author.Value); } Console .ReadKey(); } } } Please refer the below links http://www.dotnetperls.com/hashtable http://www.c-sharpcorner.com/UploadFile/mahesh/dictionary-in-C-Sharp/ http://www.dotnetperls.com/dictionary http://www.c-sharpcorner.com/uploadfile/niradhip/dictionary-in-C-Sharp/

Vulpes · Answer

Dictionary is strongly typed and Hashtable is weakly typed. This means that Dictionary stores the key/value pairs internally as their actual types. However, Hashtable stores them as type System.Object. Consequently, when using Hashtable, you always need to cast the values from object to their actual type in order to be able to do anything useful with them. Worse still, if the key or value is a value type (such as int, double, bool etc), then it needs to be 'boxed' on the heap - a relatively slow operation - so that it can be stored as System.Object. This means that Hashtable is slower than Dictionary where value types are concerned.