How to create a Hashtable?

How to remove elements from the hashtable?

The Hashtable class provides 16 different types of constructors that are used to create a hashtable, here we only use Hashtable() constructor. To read more about Hashtable’s constructors you can refer to C# | Hashtable Class This constructor is used to create an instance of the Hashtable class which is empty and has the default initial capacity, load factor, hash code provider, and comparer. Now, let’s see how to create a hashtable using Hashtable() constructor:

Step 1: Include System. Collections namespace in your program with the help of using keyword:

using System.Collections;

Step 2: Create a hashtable using Hashtable class as shown below:

Hashtable hashtable_name = new Hashtable();

Step 3: If you want to add a key/value pair in your hashtable, then use Add() method to add elements in your hashtable. And you can also store a key/value pair in your hashtable without using Add() method.

Example:

C#

// C# program to illustrate how
// to create a hashtable
using System;
using System.Collections;
 
class GFG {
 
    // Main Method
    static public void Main()
    {
 
        // Create a hashtable
        // Using Hashtable class
        Hashtable my_hashtable1 = new Hashtable();
 
        // Adding key/value pair 
        // in the hashtable
        // Using Add() method
        my_hashtable1.Add("A1", "Welcome");
        my_hashtable1.Add("A2", "to");
        my_hashtable1.Add("A3", "w3wiki");
 
        Console.WriteLine("Key and Value pairs from my_hashtable1:");
 
        foreach(DictionaryEntry ele1 in my_hashtable1)
        {
            Console.WriteLine("{0} and {1} ", ele1.Key, ele1.Value);
        }
 
        // Create another hashtable
        // Using Hashtable class
        // and adding key/value pairs
        // without using Add method
        Hashtable my_hashtable2 = new Hashtable() {
                                      {1, "hello"},
                                          {2, 234},
                                        {3, 230.45},
                                         {4, null}};
 
        Console.WriteLine("Key and Value pairs from my_hashtable2:");
 
        foreach(var ele2 in my_hashtable2.Keys)
        {
            Console.WriteLine("{0}and {1}", ele2,
                            my_hashtable2[ele2]);
        }
    }
}

Output

Key and Value pairs from my_hashtable1:
A3 and w3wiki 
A2 and to 
A1 and Welcome 
Key and Value pairs from my_hashtable2:
4and 
3and 230.45
2and 234
1and hello

C# Hashtable with Examples

A Hashtable is a collection of key/value pairs that are arranged based on the hash code of the key. In other words, a Hashtable is used to create a collection that uses a hash table for storage. It generally optimizes the lookup by calculating the hash code of every key and storing it into another basket automatically and when you access the value from the hashtable at that time it matches the hashcode with the specified key. It is the non-generic type of collection that is defined in the System. Collections namespace.

Important Points:

In Hashtable, the key cannot be null, but the value can be.
In Hashtable, key objects must be immutable as long as they are used as keys in the Hashtable.
The capacity of a Hashtable is the number of elements that Hashtable can hold.
A hash function is provided by each key object in the Hashtable.
The Hashtable class implements the IDictionary, ICollection, IEnumerable, ISerializable, IDeserializationCallback, and ICloneable interfaces.
In the hashtable, you can store elements of the same type and of the different types.
The elements of the hashtable that is a key/value pair are stored in DictionaryEntry, so you can also cast the key/value pairs to a DictionaryEntry.
that key that must be unique. Duplicate keys are not allowed.

Tags:

#CSharp-Collections-Hashtable #CSharp-Collections-Namespace #C#

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