Dfference between an Array and ArrayList in dotnet framework

Feature	Array	ArrayList
Type Safety	Strongly typed	Weakly typed (stores object)
Resizable	? Fixed size	? Automatically resizes
Performance	Faster (no boxing/unboxing)	Slower (boxing/unboxing for value types)
Generics Support	? (Use T[])	? (Use List instead)
Usage Recommendation	Use for fixed-size, typed data	Use List instead of ArrayList

 

Conceptual Differences

?? 1. Array

• Declared with a specific type and fixed size.

• Example:
   

  int[] numbers = new int[3];
  numbers[0] = 1;
  numbers[1] = 2;
  

   

• Benefits:

  • Type safety (compile-time checking).

  • Better performance for value types.

• Limitations:

  • Size is fixed after creation.

  • Can't mix different data types.

 

2. ArrayList

• Part of System.Collections (non-generic).

• Stores elements as object, allowing mixed types (not recommended).

• Example:
   

  ArrayList list = new ArrayList();
  list.Add(1);          // boxed int
  list.Add("hello");    // string
  

  Drawbacks:

• Boxing/unboxing overhead with value types.

• No compile-time type checking.

 Example Comparison

// Array (strongly typed)
int[] ages = new int[2];
ages[0] = 25;
ages[1] = 30;

// ArrayList (weakly typed)
ArrayList data = new ArrayList();
data.Add(25);        // boxed
data.Add("John");    // allowed, but dangerous
int age = (int)data[0];  // requires casting

 

Should You Use ArrayList?
No — use List instead (from System.Collections.Generic).

List list = new List();
list.Add(10);  // no boxing
int num = list[0];  // no casting needed

In Summary:
 

Use Case	Recommended Type
Fixed-size, performance-critical	Array
Dynamic, type-safe collection	List
Legacy non-generic collections	ArrayList (not recommended)