C# ArrayList - TrimToSize() Method

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The C# ArrayList TrimToSize() method is used to set the capacity to the actual number of elements in the ArrayList.

This method can reduce the memory overhead of a collection if no new elements are added to it.

This method takes O(n) operation, where n is the number of elements.

Syntax

Following is the syntax of the C# ArrayList TrimToSize() method −

public virtual void TrimToSize();

Parameters

This method does not accepts any parameters.

Return value

This method does not return any value.

Example 1: Demonstrate the Use of TrimToSize() Method

Following is the basic example of the TrimToSize() method to demonstrate how to use this method −

using System;
using System.Collections;

class Example {

   // Main method
   public static void Main() {
   
      // create and initialize new ArrayList
      ArrayList mylist = new ArrayList {
         "Hi",
         "tutorialspoint",
         "India",
         "Learn",
         "programming",
         "here"
      };
   
      // Size of ArrayList before trimming
      Console.WriteLine("Before trimming the capacity is: {0}", mylist.Capacity);
   
      mylist.TrimToSize();
   
      // Size of ArrayList after trimming
      Console.WriteLine("After trimming the capacity is: {0}", mylist.Capacity);
   }
}

Output

Following is the output −

Before trimming the capacity is: 8
After trimming the capacity is: 6

Example 2: Trimming the ArrayList Size

Here, in this example, we create an ArrayList with a specified size. We then use the TrimToSize() method to set the capacity to the actual number of elements in the ArrayList −

using System;
using System.Collections;
class Program
{
   static void Main()
   {
      // Creating an ArrayList with an initial capacity
      ArrayList myList = new ArrayList(10) { 1, 2, 3, 4, 5 };

      Console.WriteLine($"Capacity before TrimToSize: {myList.Capacity}");
      Console.WriteLine($"Count: {myList.Count}");

      // Trimming the ArrayList to fit the actual number of elements
      myList.TrimToSize();

      Console.WriteLine($"Capacity after TrimToSize: {myList.Capacity}");
   }
}

Output

Following is the output −

Capacity before TrimToSize: 10
Count: 5
Capacity after TrimToSize: 5

Example 3: Trimming After Removing Elements

This example shows how the TrimToSize() method is useful after removing elements from an ArrayList −

using System;
using System.Collections;
class Example
{
   static void Main()
   {
      ArrayList list = new ArrayList() { 10, 20, 30, 40, 50, 60, 70, 80 };
      
      Console.WriteLine($"Capacity before removing elements: {list.Capacity}");
      Console.WriteLine($"Count: {list.Count}");
      
      // Removing elements
      list.RemoveRange(2, 4);
      Console.WriteLine($"Capacity before TrimToSize: {list.Capacity}");
      Console.WriteLine($"Count after removal: {list.Count}");
      
      // Trimming the list to fit the remaining elements
      list.TrimToSize();
      Console.WriteLine($"Capacity after TrimToSize: {list.Capacity}");
   }
}

Output

Following is the output −

Capacity before removing elements: 8
Count: 8
Capacity before TrimToSize: 8
Count after removal: 4
Capacity after TrimToSize: 4

Example 4: Dynamic TrimToSize Usage

This example shows adding multiple elements dynamically, removing some, and then trimming the ArrayList to free unused memory −

using System;
using System.Collections;

class Example
{
   static void Main()
   {
      ArrayList numbers = new ArrayList();
      for (int i = 1; i <= 8; i++)
      {
          numbers.Add(i);
      }
      
      Console.WriteLine($"Capacity before removing elements: {numbers.Capacity}");
      Console.WriteLine($"Count before removing elements: {numbers.Count}");
      
      // Remove some elements
      numbers.RemoveRange(5, 2);
      
      Console.WriteLine($"Capacity before TrimToSize: {numbers.Capacity}");
      Console.WriteLine($"Count after removal: {numbers.Count}");
      
      // Trim the ArrayList to free unused memory
      numbers.TrimToSize();
      
      Console.WriteLine($"Capacity after TrimToSize: {numbers.Capacity}");
   }
}

Output

Following is the output −

Capacity before removing elements: 8
Count before removing elements: 8
Capacity before TrimToSize: 8
Count after removal: 6
Capacity after TrimToSize: 6