What is the difference between ArrayList and List in C#?

The differences between ArrayList and List in C# are as follows:

• Typing:

  • ArrayList stores elements of type object (non-generic collection), which requires casting when retrieving elements and reduces type safety.
  • List<T> is a generic collection (T is a specified type), stores elements of a strictly defined type, ensuring type safety and eliminating the need for casting.

• Performance:

  • Adding and retrieving elements in ArrayList can be slower due to boxing and unboxing of value types.
  • List<T> is generally faster, especially for value types, as it avoids boxing/unboxing.

• Type Safety:

  • ArrayList can contain elements of different types, which may lead to runtime errors.
  • List<T> provides compile-time type safety.

• Implementation:

  • ArrayList resides in the System.Collections namespace.
  • List<T> resides in the System.Collections.Generic namespace.

• Usage:

  • ArrayList is considered obsolete and is not recommended for use in new code.
  • List<T> is the preferred choice for most scenarios.

Example usage:

// Using ArrayList
System.Collections.ArrayList arrayList = new System.Collections.ArrayList();
arrayList.Add(1);       // int is boxed into object
arrayList.Add("string"); // string is stored as object

int number = (int)arrayList[0]; // Casting is required

// Using List<T>
System.Collections.Generic.List<int> list = new System.Collections.Generic.List<int>();
list.Add(1); // Adding int

// int number = list[0]; // No casting needed

Comparison table:

Attribute	ArrayList	List<T>
Typing	Non-typed (object)	Generic (T)
Performance	Possible boxing/unboxing	Higher, no boxing/unboxing for value types
Type Safety	Low	High (at compile time)
Namespace	System.Collections	System.Collections.Generic
Recommendation	Not recommended	Recommended