Clear a Hashtable in C#

Parameters

The Clear() method takes no parameters.

Return Value

The Clear() method does not return any value. It is a void method that modifies the Hashtable in place.

Using Clear() to Empty a Hashtable

Example

using System;
using System.Collections;

public class Demo {
   public static void Main() {
      Hashtable h = new Hashtable();
      h.Add(1, "Amit");
      h.Add(2, "Sachin");
      h.Add(3, "Rahul");
      
      Console.WriteLine("Keys and Values list:");
      foreach (var key in h.Keys) {
         Console.WriteLine("Key = {0}, Value = {1}", key, h[key]);
      }
      
      Console.WriteLine("Count before Clear(): " + h.Count);
      
      // clear all key value pairs
      h.Clear();
      
      Console.WriteLine("Count after Clear(): " + h.Count);
      Console.WriteLine("The Hashtable is now empty.");
      
      foreach (var key in h.Keys) {
         Console.WriteLine("Key = {0}, Value = {1}", key, h[key]);
      }
   }
}

The output of the above code is −

Keys and Values list:
Key = 3, Value = Rahul
Key = 2, Value = Sachin
Key = 1, Value = Amit
Count before Clear(): 3
Count after Clear(): 0
The Hashtable is now empty.

Clear() vs Creating New Hashtable

Example

using System;
using System.Collections;

public class ClearComparison {
   public static void Main() {
      // Method 1: Using Clear()
      Hashtable h1 = new Hashtable();
      h1.Add("A", 100);
      h1.Add("B", 200);
      Console.WriteLine("Before Clear() - Count: " + h1.Count);
      h1.Clear();
      Console.WriteLine("After Clear() - Count: " + h1.Count);
      
      // Method 2: Creating new Hashtable
      Hashtable h2 = new Hashtable();
      h2.Add("X", 300);
      h2.Add("Y", 400);
      Console.WriteLine("Before reassignment - Count: " + h2.Count);
      h2 = new Hashtable();
      Console.WriteLine("After reassignment - Count: " + h2.Count);
   }
}

The output of the above code is −

Before Clear() - Count: 2
After Clear() - Count: 0
Before reassignment - Count: 2
After reassignment - Count: 0

Comparison

Conclusion

The Clear() method efficiently removes all key-value pairs from a Hashtable, setting its count to zero while preserving the original capacity. This method is preferred when you need to reuse the same Hashtable object for new data.