What is Array List and Hash Tables?

Question

What is Array List and Hash Tables? Please Tell me With Examples.

Satyapriya Nayak · Answer

Hi Magesh Arraylist is a collection of objects(may be of different types). Arraylist is very much similar to array but it can take values of different datatypes.If you want to find something in a arraylist you have to go through each value in arraylist theres no faster way out. Program that uses ArrayList [C#] using System.Collections; class Program { static void Main() { // // Create an ArrayList and add three elements. // ArrayList list = new ArrayList (); list.Add(One); list.Add(Two); list.Add(Three); } } 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); } } } Please refer the below links http://www.dotnetperls.com/arraylist http://www.dotnetperls.com/hashtable Thanks

Sam Hobbs · Answer

For some reason hash tables get a lot of attention in this web site but I have not seen a situation described in which hash tables are a better choice then other relevant collections. Hash tables were designed when main memory and disk drives were slower and were much more expensive. When hash tables were designed most computers had less than a megabyte of memory. Your computer and every modern Windows system has more than a thousand times more memory. Don't compare hash tables to ArrayLists; the Dictionary and SortedList classes are more relevant. The way that a hash table works is that for each itme in th list a hash is generated. The hash is not intended to be unique for each item; it just is supposed to determine where an item is approximately so it is not necessary to search all items. Other collections such as dictionaries store items in a manner such that items can be found quiclly and precisely and you do not need to add code to do that. With hash tables when a hash is not unique you have to have code to deal with that.