ArrayList and LinkedList in Java, both implement the List interface and their methods and results are almost identical. The main difference between them comes from the way they internally store the elements. ArrayList is a dynamically resizing array, which means the elements are stored in adjacent memory locations and thereby allows constant time O(1) access to any elements as you can calculate offset directly. When an ArrayList grows beyond the capacity, a new array is created and the old data is moved to the new space, which can be a significant overhead for large arrays. LinkedList, on the other hand, is made up of nodes where each node contains a reference to the data and the next node in the list. These nodes are not stored in adjacent memory spaces. Therefore, adding or removing an element only requires changing the node link, making these operations have constant time complexity O(1), assuming you have direct access to the node which usually is not the case. Because of the need to traverse the list from the start to our desired index, access time in LinkedList is O(n). So, in general: - Use ArrayLists when you want good performance with random access of elements. - Use LinkedLists when your primary use case is adding and removing a lot of elements and you don't need to access elements randomly often. However, it’s important to note that ArrayList almost always outperforms LinkedList in practice, even in use-cases where LinkedList theoretically should be faster, because modern CPU architecture favors contiguous memory access. In summary, ArrayList should be the default choice and LinkedList should only be used in very specific cases.