C# - Hashtables?

Author

Hashtables?

Kevin Parkinson

2004-03-28, 11:32 pm

Hello Everyone:
I am new to this newsgroup and to C#, Although I have a little
experience with C++ and Java. Can anyone offer a simple explanation of what
a hashtable is?

Is it simply a table that maps keys to values, or is that only one
implementation? Thank you.

Kevin Parkinson

djrb

2004-03-29, 6:51 pm

A Hashtable is a data structure that supports very fast (almost
constant time)
addition, removal and lookup of data. Each stored value has a
corresponding key which uniqely identifies the value. So you can think
of data, stored in a Hashtable, as a <key, value> pairs.

The amount of time that is required for a Hashtable to accomplish
Add(k,v), Remove(k) and Lookup(k) is strongly dependent on the hash
function that is used to hash the keys. There is a lot of theory
behind that issue.
I think hashatbles are well covered in following book,
http://www.amazon.com/exec/obidos/t...179159?v=glance
(but that is only a guess).

In C# System.Collections.Hashtable implements a not synchronized
Hashtable.
Most popular methods for me are Add, Remove and the values indexer
that returns a value upon a key, like in following example:

using System.Collections;

void Main()
{
Hashtable h = new Hashtable();
Data d = new Data();
int key = 1000;

h.Add(key, d);

Data fromhashtable = h[1000]; // will return d
....
....
}

For synchronization purposes see the static Synchronized method of
class
Hashtable. Check out the lines about thread-safe enumeration.

I think that is it.

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