ArrayList and LinkedList both implements List interface and their methods and results are almost identical. However there are few differences between them which make one better over another depending on the requirement.
ArrayList Vs LinkedList
1) Search: ArrayList search operation is pretty fast compared to the LinkedList search operation. get(int index) in ArrayList gives the performance of O(1) while LinkedList performance is O(n).
Reason: ArrayList maintains index based system for its elements as it uses array data structure implicitly which makes it faster for searching an element in the list. On the other side LinkedList implements doubly linked list which requires the traversal through all the elements for searching an element.
2) Deletion: LinkedList remove operation gives O(1) performance while ArrayList gives variable performance: O(n) in worst case (while removing first element) and O(1) in best case (While removing last element).
Conclusion: LinkedList element deletion is faster compared to ArrayList.
Reason: LinkedList’s each element maintains two pointers (addresses) which points to the both neighbor elements in the list. Hence removal only requires change in the pointer location in the two neighbor nodes (elements) of the node which is going to be removed. While In ArrayList all the elements need to be shifted to fill out the space created by removed element.
3) Inserts Performance: LinkedList add method gives O(1) performance while ArrayList gives O(n) in worst case. Reason is same as explained for remove.
4) Memory Overhead: ArrayList maintains indexes and element data while LinkedList maintains element data and two pointers for neighbor nodes hence the memory consumption is high in LinkedList comparatively.
There are few similarities between these classes which are as follows:
- Both ArrayList and LinkedList are implementation of List interface.
- They both maintain the elements insertion order which means while displaying ArrayList and LinkedList elements the result set would be having the same order in which the elements got inserted into the List.
- Both these classes are non-synchronized and can be made synchronized explicitly by using
Collections.synchronizedListmethod. - The iterator and listIterator returned by these classes are fail-fast (if list is structurally modified at any time after the iterator is created, in any way except through the iterator’s own remove or add methods, the iterator will throw a ConcurrentModificationException).
When to use LinkedList and when to use ArrayList?
1) As explained above the insert and remove operations give good performance (O(1)) in LinkedList compared to ArrayList(O(n)). Hence if there is a requirement of frequent addition and deletion in application then LinkedList is a best choice.
2) Search (get method) operations are fast in Arraylist (O(1)) but not in LinkedList (O(n)) so If there are less add and remove operations and more search operations requirement, ArrayList would be your best bet.
krishna kumar gupta says
really great explanations
Subhankar Adhikary says
I am new in java. I want to know basic difference between ArrayList and LinkList. This is nice article. Nice Job. Nice explained. Its really helps me.
vairam says
very gud explanation. Superb.
enadun says
Thanks a lot. Fully satisfied answer !
Anshuman Dwivedi says
You said –
The iterator and listIterator returned by these classes are fail-fast (if list is structurally modified at any time after the iterator is created, in any way except through the iterator’s own remove or add methods.
How are you going to add element via iterator ?
Subbareddy says
Hi,
This post is really good. But, In the above I have one doubt. while searching arraylist follows O(1) because of index. At the same time why arraylist will not follow same one while deletion.
regards,
Subbareddy
Neel Mehta says
ArrayList doesn’t follow the same for delete since even though it can find the element at the given index fairly quickly, it has to shift all the elements at the later indices back one so that the empty index of the deleted element gets filled.
Mfily says
It’s really a nice post but i want to know the definition of array list and linked list I can’t get the definition.
Prince Abhijeet says
You see: ArrayList has indexes and LinkedList has pointer to next node. So deleting an item of ArrayList will cause next items to shift left so shifting takes more time. Whereas in case of LinkedList when an item is deleted there is no need to shift left the next items, only thing is needed is to point the pointer to the next node.
Anonymous007 says
An arrayList stores data at contiguous memory locations, so when deletion operation is performed it creates an empty space in arrayList. This empty space has to be occupied again by performing large number of shift operations. And hence DELETION from arrayList does not give O(1).
robert says
why isn’t array list implemented to insert an item to the end -> so no reindexing would be needed and the insert operation would be O(1) ? If I wanted to delete an item from linked list, wouldn’t it be needed to search for the item firstly (so it would be O(n) ) ?
Michael says
Dear Robert, this is what I asked myself, too. I looked into the code and remove has O(n). If you use iterator for remove or add, then you have O(1).
See Stackoverflow: http://stackoverflow.com/questions/322715/when-to-use-linkedlist-over-arraylist
Paras Mehta says
Isn’t array list add is O(1) as it adds element at the end. Insertion order is maintained. So add should be O(1) only….
Wasim says
Superb explanation :)
Ilia says
Great, thanks! And what about editing the data? Which one is better if you change it a lot? Like if the type is integer and you constantly increase the values of the items. Sorry, if the question is stupid.