Answer by Ryan for When to use LinkedList over ArrayList in Java?

ArrayList is essentially an array. LinkedList is implemented as a double linked list.

The get is pretty clear. O(1) for ArrayList, because ArrayList allow random access by using index. O(n) for LinkedList, because it needs to find the index first. Note: there are different versions of add and remove.

LinkedList is faster in add and remove, but slower in get. In brief, LinkedList should be preferred if:

1. there are no large number of random access of element
2. there are a large number of add/remove operations

=== ArrayList ===

• add(E e)
  • add at the end of ArrayList
  • require memory resizing cost.
  • O(n) worst, O(1) amortized
• add(int index, E element)
  • add to a specific index position
  • require shifting & possible memory resizing cost
  • O(n)
• remove(int index)
  • remove a specified element
  • require shifting & possible memory resizing cost
  • O(n)
• remove(Object o)
  • remove the first occurrence of the specified element from this list
  • need to search the element first, and then shifting & possible memory resizing cost
  • O(n)

=== LinkedList ===

• add(E e)

  • add to the end of the list
  • O(1)

• add(int index, E element)

  • insert at specified position
  • need to find the position first
  • O(n)
• remove()
  • remove first element of the list
  • O(1)
• remove(int index)
  • remove element with specified index
  • need to find the element first
  • O(n)
• remove(Object o)
  • remove the first occurrence of the specified element
  • need to find the element first
  • O(n)

Here is a figure from programcreek.com (add and remove are the first type, i.e., add an element at the end of the list and remove the element at the specified position in the list.):