Why is ArrayDeque better than LinkedList

Solution 1:

Linked structures are possibly the worst structure to iterate with a cache miss on each element. On top of it they consume way more memory.

If you need add/remove of the both ends, ArrayDeque is significantly better than a linked list. Random access each element is also O(1) for a cyclic queue.

The only better operation of a linked list is removing the current element during iteration.

Solution 2:

I believe that the main performance bottleneck in LinkedList is the fact that whenever you push to any end of the deque, behind the scene the implementation allocates a new linked list node, which essentially involves JVM/OS, and that's expensive. Also, whenever you pop from any end, the internal nodes of LinkedList become eligible for garbage collection and that's more work behind the scene. Also, since the linked list nodes are allocated here and there, usage of CPU cache won't provide much benefit.

If it might be of interest, I have a proof that adding (appending) an element to ArrayList or ArrayDeque runs in amortized constant time; refer to this.

Solution 3:

All the people criticizing a LinkedList, think about every other guy that has been using List in Java probably uses ArrayList and an LinkedList most of the times because they have been before Java 6 and because those are the ones being taught as a start in most books.

But, that doesn't mean, I would blindly take LinkedList's or ArrayDeque's side. If you want to know, take a look at the below benchmark done by Brian (archived).

The test setup considers:

• Each test object is a 500 character String. Each String is a different object in memory.
• The size of the test array will be varied during the tests.
• For each array size/Queue-implementation combination, 100 tests are run and average time-per-test is calculated.
• Each tests consists of filling each queue with all objects, then removing them all.
• Measure time in terms of milliseconds.

Test Result:

• Below 10,000 elements, both LinkedList and ArrayDeque tests averaged at a sub 1 ms level.
• As the sets of data get larger, the differences between the ArrayDeque and LinkedList average test time gets larger.
• At the test size of 9,900,000 elements, the LinkedList approach took ~165% longer than the ArrayDeque approach.

Graph:

Takeaway:

• If your requirement is storing 100 or 200 elements, it wouldn't make much of a difference using either of the Queues.
• However, if you are developing on mobile, you may want to use an ArrayList or ArrayDeque with a good guess of maximum capacity that the list may be required to be because of strict memory constraint.
• A lot of code exists, written using a LinkedList so tread carefully when deciding to use a ArrayDeque especially because it DOESN'T implement the List interface(I think that's reason big enough). It may be that your codebase talks to the List interface extensively, most probably and you decide to jump in with an ArrayDeque. Using it for internal implementations might be a good idea...