System.Collections.Hashtable

Added in .NET 1.1
Consider upgrading to System.Collections.Generic.Dictionary

System.Collections.Hashtable 

This collection stores information based on their unique key
Their key has an Int21 data type and is called a hash code.
This is a collection of key/value pairs that are organised based on the hash code of the key.

System.Collections.Specialized

StringDictionary
ListDictionary
StringCollection

This is a helper class for other classes
We can use it to constomise equality operations for a type.

System.Collections.Hashtable myHashtable; 
myHashtable = new System.Collections.Hashtable(); 

myHashtable.Add("Mon", new System.DateTime(2020,10,3)); 
myHashtable.Add("Tue", new System.DateTime(2021,10,3)); 
myHashtable.Add("Wed", new System.DateTime(2022,10,3)); 

if (myHashtable.ContainsKey("Tue") 
{ 
   System.DateTime myDateTime; 
   myDateTime = (System.DateTime)myHashtable["Tue"]; 
}