Explain the difference between Array, ArrayList, and List<T>.

Array:

• Fixed size
• Type-safe
• Best performance
• Zero-based indexing
  ArrayList:
• Dynamic size
• Stores objects (boxing for value types)
• Not type-safe
• Legacy, avoid in new code
  List:
• Dynamic size
• Type-safe with generics
• No boxing for value types
• Preferred choice for dynamic collections

// Array
int[] array = new int[5];
// ArrayList (avoid)
ArrayList arrayList = new ArrayList();
arrayList.Add(1);       // Boxing occurs
arrayList.Add("text");  // No compile-time type checking
// List<T> (preferred)
List<int> list = new List<int>();
list.Add(1);           // No boxing
// list.Add("text");   // Compile-time error