Non-Generic Collection with Hashtable in C#

In this we will explore methods like Add, Contains, ContainsKey, and ContainsValue for data manipulation. Improve your understanding of data structures in C#.

Collections

C# includes various classes that store the values or objects called collections.

There are two types of collections available in C#.

Non-generic collections and Generic collections

The System. The collections namespace contains the non-generic collection types and systems.Collections.Generic namespace includes generic collection types.

In most cases, it is recommended to use the generic collections because they perform faster than non-generic collections and also minimize exceptions by giving compile-time errors.

Non-generic Collections ArrayList, Stack, Queue, Hashtable

Hashtable

A Hashtable is a collection of key/value pairs. It is the non-generic type of collection that is defined in the System. Collections namespace.

How to create?

syntax

Hashtable hashtable_name = new Hashtable();

Example

// 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", "India");

        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]);
        }
    }
}

How do you remove elements?

• Clear: This method is used to remove all the objects from the hashtable.
• Remove: This method is used to remove the element with the specified key from the hashtable.

Example

// C# program to illustrate how
// remove elements from the hashtable
using System;
using System.Collections;

class GFG {

    // Main Method
    static public void Main()
    {

        // Create a hashtable
        // Using Hashtable class
        Hashtable my_hashtable = new Hashtable();

        // Adding key/value pair
        // in the hashtable
        // Using Add() method
        my_hashtable.Add("A1", "Welcome");
        my_hashtable.Add("A2", "to");
        my_hashtable.Add("A3", "India");

        // Using remove method
        // remove A2 key/value pair
        my_hashtable.Remove("A2");

        Console.WriteLine("Key and Value pairs :");

        foreach(DictionaryEntry ele1 in my_hashtable)
        {
            Console.WriteLine("{0} and {1} ", ele1.Key, ele1.Value);
        }

        // Before using Clear method
        Console.WriteLine("Total number of elements present"+
                          " in my_hashtable:{0}", my_hashtable.Count);

        my_hashtable.Clear();

        // After using Clear method
        Console.WriteLine("Total number of elements present in"+
                          " my_hashtable:{0}", my_hashtable.Count);
    }
}

How do I check availability?

• Contains: This method is used to check whether the Hashtable contains a specific key.
• ContainsKey: This method is also used to check whether the Hashtable contains a specific key.
• ContainsValue: This method is used to check whether the Hashtable contains a specific value.

using System;
using System.Collections;

class GFG {

    // Main Method
    static public void Main()
    {

        // Create a hashtable
        // Using Hashtable class
        Hashtable my_hashtable = new Hashtable();

        // Adding key/value pair in the hashtable
        // Using Add() method
        my_hashtable.Add("A1", "Welcome");
        my_hashtable.Add("A2", "to");
        my_hashtable.Add("A3", "India");

        // Determine whether the given
        // key present or not
        // using Contains method
        Console.WriteLine(my_hashtable.Contains("A3"));
        Console.WriteLine(my_hashtable.Contains(12));
        Console.WriteLine();

        // Determine whether the given
        // key present or not
        // using ContainsKey method
        Console.WriteLine(my_hashtable.ContainsKey("A1"));
        Console.WriteLine(my_hashtable.ContainsKey(1));
        Console.WriteLine();

        // Determine whether the given
        // value present or not
        // using ContainsValue method
        Console.WriteLine(my_hashtable.ContainsValue("geeks"));
        Console.WriteLine(my_hashtable.ContainsValue("to"));
    }
}

Happy Coding!

Thanks.