What is the difference between Array and ArrayList?
💡 Concept: Array vs ArrayList
An Array is a fixed-size, strongly-typed collection of elements, while ArrayList is a dynamic, non-generic collection that can hold objects of any type.
📘 Quick Intro
Arrays provide better performance and type safety. ArrayLists offer flexibility but require casting and have boxing/unboxing overhead.
🧠 Analogy
Think of an array as a row of lockers each with a specific key (type). An ArrayList is like a flexible storage box where anything can be thrown in but you have to check what’s inside when you take it out.
🔧 Technical Explanation
- 🧱 Arrays have a fixed size and strong type checking at compile time.
- 🔄 ArrayLists are resizable and can hold objects of any type (non-generic).
- ⚠️ ArrayLists require boxing/unboxing for value types, impacting performance.
- 🎯 Arrays provide better performance and compile-time type safety.
- 🔧 Use generic collections like List<T> instead of ArrayList in modern C#.
🎯 Use Cases
- ✅ Use Arrays when the size is known and performance is critical.
- ✅ Use ArrayLists when flexibility is needed but be cautious of type safety.
- ✅ Prefer List<T> in most scenarios over ArrayList.
- ✅ Useful for legacy code compatibility.
💻 Code Example
// Array example
int[] numbers = new int[3];
numbers[0] = 1;
numbers[1] = 2;
numbers[2] = 3;
// ArrayList example
ArrayList list = new ArrayList();
list.Add(1);
list.Add("Two");
list.Add(3.0);
❓ Interview Q&A
Q1: What is the main difference between Array and ArrayList?
A: Arrays are fixed size and type-safe; ArrayLists are dynamic and not type-safe.
Q2: Can you store different types in an ArrayList?
A: Yes, because it holds objects.
Q3: Is boxing involved with ArrayLists?
A: Yes, for value types.
Q4: Which is faster, Array or ArrayList?
A: Arrays are faster due to lack of boxing and type checks.
Q5: Should you use ArrayList in new code?
A: No, prefer List<T>.
Q6: Can you resize an Array?
A: No, arrays have fixed size.
Q7: How do you add items to an ArrayList?
A: Using Add() method.
Q8: Are Arrays zero-based?
A: Yes.
Q9: Can ArrayLists store value types?
A: Yes, but boxing occurs.
Q10: What namespace contains ArrayList?
A: System.Collections.
📝 MCQs
Q1. Are Arrays fixed size?
- Yes
- No
- Sometimes
- Only in C#
Q2. Can ArrayLists hold multiple types?
- No
- Yes
- Only primitives
- Only objects
Q3. Do Arrays support boxing?
- Yes
- No
- Only in .NET 5+
- Sometimes
Q4. Which is faster, Array or ArrayList?
- ArrayList
- Array
- Same
- Depends on usage
Q5. Can Array size be changed after creation?
- Yes
- No
- Only with Resize()
- With dynamic arrays
Q6. Which collection is recommended over ArrayList?
- Array
- Hashtable
- List<T>
- Dictionary
Q7. How to add items to ArrayList?
- Add()
- Insert()
- Append()
- Push()
Q8. Are Arrays zero-based?
- Yes
- No
- Depends
- Sometimes
Q9. Does ArrayList involve boxing for value types?
- No
- Yes
- Only for reference types
- Never
Q10. Which namespace contains ArrayList?
- System.Collections
- System.Collections.Generic
- System.Array
- System.Core
💡 Bonus Insight
While ArrayList provides flexibility for heterogeneous collections, modern C# favors generic collections like List<T> for better performance and type safety.
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