Comparison of ArrayList, LinkedList, MutableList, List, Array, and Vector in Kotlin

Here’s a detailed comparison of ArrayList, LinkedList, MutableList, List, Array, and Vector in Kotlin, along with examples and key differences:

---

1. ArrayList

• Type: Mutable, backed by a dynamically resizable array.
• Use Case: When frequent random access is required and the size of the collection might change.
• Performance:
  • Access: O(1) (fast random access).
  • Insert/Delete: O(n) (due to shifting elements).
• Example:

   val arrayList = ArrayList<Int>() 
   arrayList.add(1) 
   arrayList.add(2) 
   println(arrayList) // Output: [1, 2]
  

  ---

2. LinkedList

• Type: Mutable, doubly linked list implementation.
• Use Case: When frequent insertions or deletions in the middle of the list are required.
• Performance:
  • Access: O(n) (no random access).
  • Insert/Delete: O(1) for adding/removing elements at the head or tail.
• Example:

    val linkedList = java.util.LinkedList<Int>() // Use Java's LinkedList
    linkedList.add(1) 
    linkedList.add(2) 
    println(linkedList) // Output: [1, 2]
  

  ---

3. MutableList

• Type: Interface, represents a mutable collection of elements.
• Use Case: When you want to modify the list (add/remove elements). Can be implemented by ArrayList or LinkedList.
• Performance: Depends on the underlying implementation (e.g., ArrayList, LinkedList).
• Example:

  val mutableList: MutableList<Int> = mutableListOf(1, 2, 3)
  mutableList.add(4) 
  println(mutableList) // Output: [1, 2, 3, 4]
  

  ---

4. List

• Type: Interface, represents an immutable collection of elements.
• Use Case: When you don’t want to modify the list after creation.
• Performance: Depends on the underlying implementation (e.g., ArrayList, LinkedList).
• Example:

  val list: List<Int> = listOf(1, 2, 3) // list.add(4) // Compilation error: Cannot add to an immutable list println(list) // Output: [1, 2, 3]
  

  ---

5. Array

• Type: Fixed-size, strongly-typed collection of elements.
• Use Case: When you know the size of the collection at compile time and don’t need resizing.
• Performance:
  • Access: O(1) (fast random access).
  • Insert/Delete: O(n) (no dynamic resizing).
• Example:

  val array = arrayOf(1, 2, 3) 
  array[0] = 10 
  println(array.joinToString()) // Output: 10, 2, 3
  

  ---

6. Vector

• Type: Thread-safe mutable collection, backed by a dynamically resizable array (from Java).
• Use Case: When thread-safe operations on a collection are required.
• Performance:
  • Access: O(1) (fast random access).
  • Insert/Delete: O(n) (similar to ArrayList).
  • Slower than ArrayList due to synchronization overhead.
• Example:

  val vector = java.util.Vector<Int>() 
  vector.add(1) 
  vector.add(2) 
  println(vector) // Output: [1, 2]
  

  ---

Comparison Table

Type	Mutability	Thread-Safe	Access Performance	Insert/Delete Performance	Resizable	Fixed-Size
ArrayList	Mutable	No	O(1)	O(n)	Yes	No
LinkedList	Mutable	No	O(n)	O(1) for head/tail	Yes	No
MutableList	Mutable	No	Depends on implementation	Depends on implementation	Yes	No
List	Immutable	No	Depends on implementation	Immutable (no modification)	Yes	No
Array	Mutable	No	O(1)	O(n)	No	Yes
Vector	Mutable	Yes	O(1)	O(n)	Yes	No

---

Key Points:

• Use ArrayList for most general-purpose collections when random access is needed.
• Use LinkedList when frequent insertions and deletions are required.
• Use MutableList or List based on whether you need mutability.
• Use Array for fixed-size collections with better performance.
• Use Vector for thread-safe collection needs.

Note:

• List and MutableList cover almost all use cases in Kotlin. Their design aligns perfectly with Kotlin’s philosophy of simplicity and immutability by default. Unless you have a very specific requirement (e.g., low-level optimizations, thread-safety, or constant insertion/deletion at specific positions), these two are enough.
• List internal implementation:

  fun <T> listOf(vararg elements: T): List<T> {
    val list = Arrays.asList(*elements)  // Creates a fixed-size list from the provided elements
    return Collections.unmodifiableList(list)  // Wraps it to prevent structural modifications
  }
  

• MutableList:

  fun <T> mutableListOf(vararg elements: T): MutableList<T> {
    val list = ArrayList<T>(elements.size)  // Creates an empty mutable list
    Collections.addAll(list, *elements)    // Adds elements to the list
    return list  // Returns the mutable list
  }