How does a Hashtable internally maintain

Manish Singh

Hi..

Ques : Hello friend now I an working collection in a .NET. In a collection i am using Hashtable but i am not understaind How does a Hashtable internally maintain the key-value pairs?

3 Replies

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Sam Hobbs14y ago
You can learn a lot using Visual Studio. In a program that you are using a Hashtable, put the cursor on "Hashtable" and press F12.
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Jignesh Trivedi14y ago
hi,

A HashTable collection stores a (Key, Value) pair and uses the Key to hash and obtain the storage location. The Key is immutable and cannot have duplicate entries in the HashTable. This sample uses several instances of a simple Person class to store in a HashTable. The last name is used as the Key.

hope this help.
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Vulpes14y ago
When you add a key and value to a Hashtable, then they're stored internally in something called a bucket. This is a nested struct within the Hashtable class which (courtesy of Redgate Reflector) looks like this:

[StructLayout(LayoutKind.Sequential)]
private struct bucket
{
public object key;
public object val;
public int hash_coll;
}

Notice that both the key and value are stored as 'object' regardless of their actual type.

Internally, the Hashtable maintains an array of these buckets and which bucket the key/value pair goes into depends on the hash value of the key.

For more detail on how all this works, I'd read the MSDN docs for the Hashtable class:

http://msdn.microsoft.com/en-us/library/system.collections.hashtable.aspx

Contrary to what it says there, the key/value pairs are not actually stored in DictionaryEntry objects but these objects are created when the Hashtable needs to be iterated.
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