Difference Between ArrayList and LinkedList

ArrayList and LinkedList both implement the List interface, so they have the same methods and both keep elements in insertion order. The difference is how they store the elements. ArrayList uses a resizable array, while LinkedList uses doubly linked nodes. This one difference decides which operations are fast and which are slow. In this lesson, you will learn all the differences and how to choose between them.

Internal Structure

• ArrayList: elements sit side by side in one array. The position of element i is calculated directly, so get(i) is instant.
• LinkedList: each element lives in a separate node object. To reach element i, the list walks from the nearer end.

Differences Between ArrayList and LinkedList

Example: Measuring the Difference

Let's see an example that times two operations on both lists. Times change from run to run, so the output is only a sample.

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
 
public class ListTiming {
    static long time(Runnable task) {
        long start = System.nanoTime();
        task.run();
        return (System.nanoTime() - start) / 1_000_000;
    }
 
    public static void main(String[] args) {
        int n = 50_000;
        List<Integer> array = new ArrayList<>();
        List<Integer> linked = new LinkedList<>();
 
        System.out.println("Add " + n + " at the front:");
        System.out.println("  ArrayList  " + time(() -> {
            for (int i = 0; i < n; i++) array.add(0, i);
        }) + " ms");
        System.out.println("  LinkedList " + time(() -> {
            for (int i = 0; i < n; i++) linked.add(0, i);
        }) + " ms");
 
        System.out.println("Get " + n + " by index:");
        System.out.println("  ArrayList  " + time(() -> {
            for (int i = 0; i < n; i++) array.get(i);
        }) + " ms");
        System.out.println("  LinkedList " + time(() -> {
            for (int i = 0; i < n; i++) linked.get(i);
        }) + " ms");
    }
}

Add 50000 at the front:
  ArrayList  62 ms
  LinkedList 1 ms
Get 50000 by index:
  ArrayList  0 ms
  LinkedList 903 ms

Explanation: Adding at the front forces ArrayList to shift every element each time, while LinkedList just links a new node. Getting by index is the opposite: ArrayList jumps straight to the slot, while LinkedList walks up to 25,000 nodes for each get.

Common Mistakes

Picking LinkedList for "fast inserts" and then inserting by index. Finding the index is the slow part.

Using an index loop over a LinkedList. Use a for-each loop or an iterator.

Ignoring memory. A LinkedList of a million elements creates a million node objects.

Interview Corner

Practice

1. Easy: Change the timing program to remove 50,000 elements from the front of each list. Which is faster, and why?
2. Harder: Time iterating over both lists with a for-each loop. Explain why both are fast, unlike get(i) on a LinkedList.

Key Takeaways