Java: What is the difference between ArrayList and LinkedList in Java?

ArrayList — dynamic array. LinkedList — doubly linked list.

ArrayList:

• Dynamic array.
• Random access O(1).
• Insert/delete middle O(n).
• Cache-friendly.

1ArrayList<Integer> list = new ArrayList<>();
2list.add(1);
3list.get(0);  // O(1) random access
4list.add(0, 10);  // O(n) - shift elements

LinkedList:

• Doubly linked list.
• Sequential access O(n).
• Insert/delete O(1) (if at position).
• Cache-unfriendly.

1LinkedList<Integer> list = new LinkedList<>();
2list.add(1);
3list.get(0);  // O(n) - traverse
4list.addFirst(10);  // O(1)

When to use:

• ArrayList — most cases, random access.
• LinkedList — frequent insert/delete.