When would you choose to use LinkedList over ArrayList in an application MCQ

Btw, if you are new to Java's collections framework then I suggest you first go throughJava Fundamentals: Collectionsby Richart Warburton. It's an online Java course on Pluralsight, which you can avail of free by signing their 10-day free trial. IMHO, it's worth going through that course to learn Java collections in the right way.

2) Both ArrayList and LinkedList are not synchronized, which means you can not share them between multiple threads without external synchronization. See here to know How to make ArrayList synchronized in Java.

3) ArrayList and LinkedList are ordered collection e.g. they maintain insertion order of elements i.e. the first element will be added to the first position.


4) ArrayList and LinkedList also allow duplicates and null, unlike any other List implementation e.g. Vector.

5) An iterator of both LinkedList and ArrayList are fail-fast which means they will throw ConcurrentModificationException if a collection is modified structurally once the Iterator is created. They are different than CopyOnWriteArrayList whose Iterator is fail-safe.

Difference between LinkedList and ArrayList in Java

Now let's see some differences between ArrayList and LinkedList and when to use ArrayList and LinkedList in Java.


1. Underlying Data Structure
The first difference between ArrayList and LinkedList comes with the fact that ArrayList is backed by Array while LinkedList is backed by LinkedList. This will lead to further differences in performance.


2. LinkedList implements Deque
Another difference between ArrayList and LinkedList is that apart from the List interface, LinkedList also implements theDeque interface, which provides first in first out operations for add() and poll() and several other Deque functions.

Also, LinkedList is implemented as a doubly-linked list and for index-based operation, navigation can happen from either end (seeComplete Java MasterClass).


3. Adding elements in ArrayList
Adding an element in ArrayList is O(1) operation if it doesn't trigger re-size of Array, in which case it becomes O(log(n)), On the other hand, appending an element in LinkedList is O(1) operation, as it doesn't require any navigation.


4. Removing an element from a position
In order to remove an element from a particular index e.g. by calling remove(index), ArrayList performs a copy operation which makes it close to O(n) while LinkedList needs to traverse to that point which also makes it O(n/2), as it can traverse from either direction based upon proximity.


5. Iterating over ArrayList or LinkedList
Iteration is the O(n) operation for both LinkedList and ArrayList where n is a number of an element.


6. Retrieving element from a position
The get(index) operation is O(1) in ArrayList while its O(n/2) in LinkedList, as it needs to traverse till that entry. Though, in Big O notation O(n/2) is just O(n) because we ignore constants there.

If you want to learn more about how to calculate time and space complexity for your algorithms using Big O notation, I recommend reading Grokking Algorithms by Aditya Bhargava, one of the most interestingbooks on this topic I have read ever.

7. Memory
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 like 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 the 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 an O(n) operation. For example, inserting or deleting an element in the middle of a linked list.

In my opinion, use ArrayList over LinkedList for most of the practical purposes in Java.


Further Learning
Java In-Depth: Become a Complete Java Engineer

Collection in Java - Educative
Algorithms and Data Structures - Part 1 and 2

Other Java Collection Articles you may like

• How to sort a Map by keys and values in Java? (tutorial)
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Thanks for reading this article so far, if you like this article then please share it with your friends and colleagues. If you have any questions or doubts then please drop a note.

P. S. -If you are keen to learn Java Programming in-depth but looking for free online courses then you can also check outJava Tutorial for Complete Beginners (FREE)course on Udemy. It's completely free and you just need an Udemy account to join this course.

An array is a collection of items stored at contiguous memory locations. The idea is to store multiple items of the same type together. However, the limitation of the array is that the size of the array is predefined and fixed. There are multiple ways to solve this problem. In this article, the difference between two classes that are implemented to solve this problem named ArrayList and LinkedList is discussed.

ArrayList is a part of the collection framework. It is present in the java.util package and provides us dynamic arrays in Java. Though, it may be slower than standard arrays but can be helpful in programs where lots of manipulation in the array is needed. We can dynamically add and remove items. It automatically resizes itself. The following is an example to demonstrate the implementation of the ArrayList.

Example

LinkedList is a linear data structure where the elements are not stored in contiguous locations and every element is a separate object with a data part and address part. The elements are linked using pointers and addresses. Each element is known as a node. Due to the dynamicity and ease of insertions and deletions, they are preferred over the arrays. The following is an example to demonstrate the implementation of the LinkedList.

Note: This class implements the LinkedList Data Structure.

Example

Now after having an adequate understanding of both of them let us do discuss the differences between ArrayList and LinkedList in Java

ArrayList LinkedList

This class uses a dynamic array to store the elements in it. With the introduction of generics, this class supports the storage of all types of objects.	This class uses a doubly linked list to store the elements in it. Similar to the ArrayList, this class also supports the storage of all types of objects.
Manipulating ArrayList takes more time due to the internal implementation. Whenever we remove an element, internally, the array is traversed and the memory bits are shifted.	Manipulating LinkedList takes less time compared to ArrayList because, in a doubly-linked list, there is no concept of shifting the memory bits. The list is traversed and the reference link is changed.
This class implements a List interface. Therefore, this acts as a list.	This class implements both the List interface and the Deque interface. Therefore, it can act as a list and a deque.
This class works better when the application demands storing the data and accessing it.	This class works better when the application demands manipulation of the stored data.

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Arrays Vs Linked Lists