What is HashTable?
C# includes Hashtable collection in System.Collections namespace, which is similar to generic collection. The Hashtable collection stores key-value pairs. It optimizes lockups by computing the hash code of each key and stores it in a different bucket internally and then matches the hash code of the specified key at the time of accessing values.
Properties of Hashtable
Count: Gets the total count of key/value pairs in the Hashtable.IsReadOnly: Gets boolean value indicating whether the Hashtable is read-only.
Item :Gets or sets the value associated with the specified key.
Keys :Gets an ICollection of keys in the Hashtable.
Values : Gets an ICollection of values in the Hashtable
Methods of HashTable
Add : The Add() method adds an item with a key and value into the Hashtable. Key and value can be of any data type. Key cannot be null whereas value can be null.
Example
static void Main(string[] args)
{
Hashtable ht = new Hashtable();
ht.Add(1, "One");
ht.Add(2, 2);
ht.Add(3, 3.0);
ht.Add(4, null);
}
Remove: Removes the item with the specified key from the hashtable.
Example
static void Main(string[] args)
{
Hashtable ht = new Hashtable();
ht.Add(1, "One");
ht.Add(2, 2);
ht.Add(3, 3.0);
ht.Add(4, null);
ht.Remove(1);
}
Clear: Removes all the items from the hashtable.
Example
static void Main(string[] args)
{
Hashtable ht = new Hashtable();
ht.Add(1, "One");
ht.Add(2, 2);
ht.Add(3, 3.0);
ht.Add(4, null);
ht.Clear();
}
Contains: Checks whether the hashtable contains a specific key.
Example
static void Main(string[] args)
{
Hashtable ht = new Hashtable();
ht.Add(1, "One");
ht.Add(2, 2);
ht.Add(3, 3.0);
ht.Add(4, null);
ht.Contains(1);//return true;
ht.Contains(1);//return true;
ht.Contains(5); //return false
}
ContainsKey: Checks whether the hashtable contains a specific key it work similar as Contains.
ContainsValue: Checks whether the hashtable contains a specific value.
static void Main(string[] args)
{
Hashtable ht = new Hashtable();
ht.Add(1, "One");
ht.Add(2, 2);
ht.Add(3, 3.0);
ht.Add(4, null);
ht.ContainsValue(5); //return true
}
GetHash: Returns the hash code for the specified key.
Summary:
- Hashtable stores key-value pairs of any datatype where the Key must be unique.
- The Hashtable key cannot be null whereas the value can be null.
- Hashtable retrieves an item by comparing the hashcode of keys. So it is slower in performance than Dictionary collection.
- Hashtable uses the default hashcode provider which is object.GetHashCode(). You can also use a custom hashcode provider.
- Use DictionaryEntry with foreach statement to iterate Hashtable.
Nice👍👏
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