20) what is the difference between arraylist and linkedlist

It is mainly the performance in specific scenarios which dictates whether to go with ArrayList or with LinkedList. While using ArrayList we generally use add method, very rarely we use add method where index is also passed to add element at any specific position in the ArrayList and to fetch elements from List we use get int index which also is faster in ArrayList.

That's why we normally use ArrayList, even JavaDocs advocate the same thing-. If you have any doubt or any suggestions to make please drop a comment. Can we not use ListIterator to iterate the ArrayList in the reverse order? Yes you can. See an example here ListIterator in Java.

ArrayList Vs LinkedList in Java 1- If we have to list the differences between the LinkedList and ArrayList in Java, first difference is in the implemenation itself- LinkedList is implemented using a doubly linked list concept where as ArrayList internally uses an array of Objects which can be resized dynamically.

Adding an element - If you are frequently adding element at the beginning of the list then LinkedList may be a better choice because in case of ArrayList adding at the beginning every time will result in shuffling all the existing elements within the underlying array by one index to create space for the new element.

In the case of adding at the last ArrayList may give O N performance in the worst case. That will happen if you add more elements than the capacity of the underlying array, as in that case a new array 1. In LinkedList adding or insertion is O 1 operation. While in ArrayList , if the array is the full i.

In LinkedList , there are two overloaded remove methods. The other overloaded remove method in LinkedList is remove int or remove Object which removes the Object or int passed as a parameter. This method traverses the LinkedList until it found the Object and unlink it from the original list. Hence this method runtime is O n. While in ArrayList remove int method involves copying elements from the old array to new updated array, hence its runtime is O n.

If the constructor is not overloaded, then ArrayList creates an empty list of initial capacity 10, while. Memory overhead in LinkedList is more as compared to ArrayList as a node in LinkedList needs to maintain the addresses of the next and previous node.

In addition to the other good arguments above, you should notice ArrayList implements RandomAccess interface, while LinkedList implements Queue. So, somehow they address slightly different problems, with difference of efficiency and behavior see their list of methods.

ArrayList is faster to access an indexed value. It is much worse when inserting or deleting objects. To find out more, read any article that talks about the difference between arrays and linked lists. An array list is essentially an array with methods to add items etc. It is a collection of items which can be accessed through an indexer for example [0]. It implies a progression from one item to the next. You can get the same effect with an array list, but a linked list absolutely says what item is supposed to follow the previous one.

See the Java Tutorials - List Implementations. An important feature of a linked list which I didn't read in another answer is the concatenation of two lists. Important : For Java its LinkedList this is not true! See Is there a fast concat method for linked list in Java? ArrayList uses contiguous memory address compared to LinkedList which uses pointers toward the next node. So when you want to look up an element in an ArrayList is faster than doing n iterations with LinkedList.

On the other hand, insertion and deletion in a LinkedList are much easier because you just have to change the pointers whereas an ArrayList implies the use of shift operation for any insertion or deletion. If you have frequent retrieval operations in your app use an ArrayList. If you have frequent insertion and deletion use a LinkedList. This will lead to further differences in performance.

Another difference between ArrayList and LinkedList is that apart from the List interface, LinkedList also implements Deque interface, which provides first in first out operations for add and poll and several other Deque functions. In order to remove an element from a particular index e. LinkedList uses a wrapper object, Entry, which is a static nested class for storing data and two nodes next and previous while ArrayList just stores data in Array. So memory requirement seems less in the case of ArrayList than LinkedList except for the case where Array performs the re-size operation when it copies content from one Array to another.

If Array is large enough it may take a lot of memory at that point and trigger Garbage collection, which can slow response time. From all the above differences between ArrayList vs LinkedList, It looks ArrayList is the better choice than LinkedList in almost all cases, except when you do a frequent add operation than remove , or get.

It's easier to modify a linked list than ArrayList, especially if you are adding or removing elements from start or end because linked list internally keeps references of those positions and they are accessible in O 1 time. In other words, you don't need to traverse through the linked list to reach the position where you want to add elements, in that case, addition becomes O n operation.

For example, inserting or deleting an element in the middle of a linked list. I have read the responses, but there is one scenario where I always use a LinkedList over an ArrayList that I want to share to hear opinions:. My rationale was that because it is impossible to know exactly how many results am I getting, there will be not memory wasted as in ArrayList with the difference between the capacity and actual number of elements , and there would be no time wasted trying to duplicate the capacity.

As far a ArrayList, I agree that at least you should always use the constructor with the initial capacity, to minimize the duplication of the arrays as much as possible.

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. 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.

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. Reason is same as explained for remove. Hence if there is a requirement of frequent addition and deletion in application then LinkedList is a best choice.

Operations that index into the list will traverse the list from the beginning or the end, whichever is closer to the specified index. One of the tests I saw on here only conducts the test once. But what I have noticed is that you need to run these tests many times and eventually their times will converge.

Basically the JVM needs to warm up. See the code below. However, the reason behind the linear processing time comes from two very different reasons:. In an ArrayList, you get to the element in O 1 , but actually removing or inserting something makes it O n because all the following elements need to be changed.

In a LinkedList, it takes O n to actually get to the desired element, because we have to start at the very beginning until we reach the desired index. Actually removing or inserting is constant, because we only have to change 1 reference for remove and 2 references for insert.

Which of the two is faster for inserting and removing depends on where it happens. If we are closer to the beginning the LinkedList will be faster, because we have to go through relatively few elements. If we are closer to the end an ArrayList will be faster, because we get there in constant time and only have to change the few remaining elements that follow it. When done precisely in the middle the LinkedList will be faster because going through n elements is quicker than moving n values.

Bonus: While there is no way of making these two methods O 1 for an ArrayList, there actually is a way to do this in LinkedLists. Let's say we want to go through the entire List removing and inserting elements on our way. Usually, you would start from the very beginning for each element using the LinkedList, we could also "save" the current element we're working on with an Iterator.

With the help of the Iterator, we get an O 1 efficiency for remove and insert when working in a LinkedList. Making it the only performance benefit I'm aware of where a LinkedList is always better than an ArrayList.

ArrayList is dynamic array. It can be said that it was basically created to overcome the drawbacks of arrays The LinkedList class extends AbstractSequentialList and implements List,Deque, and Queue interface. Performance arraylist. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?

Collectives on Stack Overflow. Learn more. Ask Question. Asked 12 years, 11 months ago. Active 1 month ago. Viewed 1. Improve this question. Steve Chambers See also: Array versus linked-list — Hawkeye Parker. Just see the quote from the author of LinkedList stackoverflow.

Add a comment. Active Oldest Votes. Improve this answer. One thing many people forget is that ArrayList is compact in memory which means that it's more cache friendly than LinkedList. LinkedList could be spread out all over RAM, while ArrayList is always snuggly packed together to take advantage of spacial locality. This has important real world ramifications. Since I believe it doesn't require any shifting of elements? It generally doubles the size if there is no spare capacity.

Masterfego 2, 1 1 gold badge 24 24 silver badges 32 32 bronze badges. Numeron Numeron 8, 3 3 gold badges 19 19 silver badges 45 45 bronze badges. The problem with your math is that your graph greatly exaggerates the impact. You are modelling objects which each contain only an int , so 4 or 8 bytes of data. In the linked list, there are essentially 4 "words" of overhead. Your graph thus gives the impression that linked lists use "five times" the storage of array lists.

This is wrong. The overhead is 16 or 32 bytes per object, as an additive adjustment, not a scaling factor. Why LinkedList sucks: It uses lots of small memory objects, and therefore impacts performance across the process.

Lots of small objects are bad for cache-locality. Any indexed operation requires a traversal, i. This is not obvious in the source code, leading to algorithms O n slower than if ArrayList was used. Getting good performance is tricky.

Even when big-O performance is the same as ArrayList , it is probably going to be significantly slower anyway. It's jarring to see LinkedList in source because it is probably the wrong choice.

Tom Hawtin - tackline Tom Hawtin - tackline k 30 30 gold badges silver badges bronze badges. Michael Munsey Michael Munsey 3, 1 1 gold badge 23 23 silver badges 14 14 bronze badges. You can't compare big-O values directly without thinking about constant factors. I don't care about small lists performance, and neither does my computer unless it is used in a loop somehow. LinkedList can't really insert in the middle in O 1. It has to run through half the list to find the insertion point.

And even worse: the end of collection. Show 9 more comments. Wouldn't another solution be managing the size of the list programmatically by using the ArrayList's ensureCapacity method? My question is why are so many things being stored in a bunch of brittle data structures when they might better be stored in a caching or db mechanism?

I had an interview the other day where they swore up and down about the evils of ArrayList, but I come here and I find that the complexity analysis is all-around better! For that increment you need 2. I'm not concerned about day to day response time, I'm worried about running out of heap memory when a peak hour hits slightly harder than it hit yesterday and a couple big arraylists deciding they need room for 2. One instance of that type of behavior during peak usage blows my sla for the whole month.

Improve Article. Like Article. Next Comparable vs Comparator in Java. Recommended Articles. Article Contributed By :. Easy Normal Medium Hard Expert. Writing code in comment? Please use ide. Load Comments. What's New.