Generic vs. Non-Generic Collections in C#: Know the Difference

When working with data structures in C#, developers often face a choice between generic and non-generic collections. Understanding their differences, advantages, and best-use scenarios is crucial for writing efficient, type-safe, and maintainable code.

In this article, we will dive deep into generic and non-generic collections in C#, explore their core differences, analyze performance impacts, and discuss best practices to ensure optimal collection usage in .NET applications.

What Are Non-Generic Collections?

Non-generic collections were introduced in .NET Framework 1.0 and reside in the System.Collections namespace. These collections store objects as object types, meaning they can hold any type of data, including value types and reference types.

Common Non-Generic Collections

ArrayList
Hashtable
Queue
Stack
SortedList

Example of Non-Generic Collection

using System;
using System.Collections;

class Program
{
    static void Main()
    {
        ArrayList list = new ArrayList();
        list.Add(1);
        list.Add("Hello");
        list.Add(3.14);

        foreach (var item in list)
        {
            Console.WriteLine(item);
        }
    }
}

Drawbacks of Non-Generic Collections

Type Safety Issue: Since elements are stored as object, type casting is required, which increases the risk of runtime exceptions.
Performance Overhead: Boxing and unboxing occur when storing value types, leading to performance inefficiencies.
Lack of Readability: Mixed data types in a collection reduce code clarity and maintainability.

What Are Generic Collections?

With the introduction of .NET 2.0, generic collections were added in the System.Collections.Generic namespace. These collections allow type safety at compile-time, eliminating the need for boxing and unboxing.

Common Generic Collections

List
Dictionary<TKey, TValue>
Queue
Stack
SortedList<TKey, TValue>

Example of Generic Collection

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List<int> numbers = new List<int>();
        numbers.Add(1);
        numbers.Add(2);
        numbers.Add(3);

        foreach (int number in numbers)
        {
            Console.WriteLine(number);
        }
    }
}

Advantages of Generic Collections

Type Safety: Generics enforce type constraints, preventing invalid data insertions.
Performance Optimization: Eliminates boxing/unboxing for value types, reducing memory overhead.
Code Maintainability: Strongly typed collections improve readability and debugging.

Performance Comparison: Generic vs. Non-Generic Collections

To illustrate the performance differences, consider a benchmark comparing ArrayList vs. List<T>:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;

class Program
{
    static void Main()
    {
        int count = 1000000;
        Stopwatch stopwatch = new Stopwatch();

        // Non-Generic Collection
        ArrayList arrayList = new ArrayList();
        stopwatch.Start();
        for (int i = 0; i < count; i++)
        {
            arrayList.Add(i);
        }
        stopwatch.Stop();
        Console.WriteLine($"ArrayList time: {stopwatch.ElapsedMilliseconds} ms");

        // Generic Collection
        List<int> genericList = new List<int>();
        stopwatch.Restart();
        for (int i = 0; i < count; i++)
        {
            genericList.Add(i);
        }
        stopwatch.Stop();
        Console.WriteLine($"List<T> time: {stopwatch.ElapsedMilliseconds} ms");
    }
}

Expected Results

The generic List<T> performs significantly faster than ArrayList.
ArrayList incurs additional overhead due to boxing/unboxing operations.
Type safety in List<T> reduces runtime errors and enhances performance.

When to Use Generic vs. Non-Generic Collections

Criteria	Generic Collections (`System.Collections.Generic`)	Non-Generic Collections (`System.Collections`)
Performance	Faster (no boxing/unboxing)	Slower due to type conversions
Type Safety	Strongly typed	Requires casting (unsafe)
Memory Usage	More efficient	Higher due to boxing/unboxing
Code Maintainability	High readability and maintainability	Low due to mixed data types
Use Case	Recommended for new development	Only for legacy support

Best Practices for Using Collections in C#

Prefer Generic Collections: Always use List<T>, Dictionary<TKey, TValue>, and other generic types for better performance and maintainability.
Minimize Boxing and Unboxing: Avoid non-generic collections when working with value types to reduce memory overhead.
Use the Right Collection Type: Choose the collection that best suits your use case (e.g., Dictionary<TKey, TValue> for key-value pairs, Queue<T> for FIFO operations).
Optimize Memory Usage: Set an initial capacity for lists if the size is known in advance to prevent unnecessary memory reallocations.
Leverage LINQ for Efficient Operations: Use LINQ methods (Where, Select, OrderBy, etc.) to improve readability and performance.

Conclusion

Choosing between generic and non-generic collections in C# is straightforward when you understand their differences. Generic collections provide superior type safety, better performance, and improved maintainability, making them the preferred choice for modern .NET applications. While non-generic collections still exist for backward compatibility, their use should be minimized in favor of generics.

By leveraging best practices and selecting the right data structures, you can write efficient, scalable, and maintainable C# applications that perform optimally in real-world scenarios.

Android, .NET & ColdFusion Tutorials