Hashtable Class

Overview

• Key-value pair based collection.
• Contains DictionaryEntry objects.
• Not accessible by index, only by key.
• Values are returned based on the hash value when doing a foreach.
• Internally uses hashes to store objects, derived from the GetHashCode method on each object.
  • Hashes and Equals are used together to decide if keys are equal.
  • No duplicate keys can occur.

Good practice

• When possible, use a generic collection instead of the object-based Hashtable.
• Implement GetHashCode and Equals in custom objects when you need Hashtable to treat objects as the same.
• Use a ListDictionary or HybridDictionary when working with collections of fewer than 10 items or of unknown size.

Examples

Adding and Removing Elements

Hashtable a = new Hashtable();
a.Add("Key1", "Hello");
a.Add("Key2", "World");
a.Add("Key0", "Start");
Console.WriteLine(a["Key1"] + " " + a["Key2"]);
foreach (DictionaryEntry d in a) { Console.WriteLine(d.Value); }
foreach (object v in a.Values) { Console.WriteLine(v); }
 
a.Remove("Key1");
foreach (object k in a.Keys) { Console.WriteLine(a[k]); }