Array vs ArrayList: Choosing the Right Data Structure

This article aims to provide a comprehensive Array vs ArrayList comparison.

Array and ArrayList are fundamental data structures in Java used for storing and manipulating collections of elements. While they have similarities, they also differ in important ways.

Similarities between Array and ArrayList.

Let us look into similarities between Array and ArrayList

Similarities	Array	ArrayList
Element Types	Both can store elements of any type.	Both can store elements of any type.
Index Access	Elements can be accessed by index.	Elements can be accessed by index.
Iteration	Both support iteration over elements.	Both support iteration over elements.
Collection Operations	Common operations such as adding, removing, and searching elements are supported.	Common operations such as adding, removing, and searching elements are supported.
Memory Efficiency	Both use contiguous memory locations to store elements.	Both use contiguous memory locations to store elements.

Key Differences : Array vs ArrayList

Let’s look into Array vs ArrayList across different criteria.

Criteria	Array	ArrayList
Resizable	Array is a fixed-length data structure.	ArrayList is a resizable array.
Creating instance with/without specifying size	It is mandatory to provide the size of the Array while creating it.	You can create an instance of ArrayList without specifying size, and Java will create it with a default size.
Primitives	Array can contain both primitives and objects.	ArrayList can only store objects, not primitives.
Operations	Arrays do not have built-in functions for these operations.	ArrayList supports additional operations like indexOf(), remove(), etc.
Generics	Generics cannot be used with Array.	ArrayList allows the use of Generics to ensure type-safety.
Performance	Array operations like add() or get() have similar performance to ArrayList.	ArrayList’s resize() operation can be slower as it involves creating a new Array and copying content.
Internal Structure	Array is a basic data structure.	ArrayList is internally backed by an Array.
Length	Array object has the length variable which returns the length of the array.	Length of the ArrayList is provided by the size() method.
Multi-dimensional	You can have a two-dimensional or a three-dimensional array.	ArrayList doesn’t allow you to specify dimensions.
Adding elements	Array uses the assignment operator to store elements.	Elements can be inserted into the ArrayList using the add() method.
Flexibility	Array is a fixed-length data structure.	ArrayList is more flexible than a plain native array because it can grow dynamically when needed.
Iteration	Array can be iterated using for or for-each loops.	ArrayList provides multiple ways for iteration, including for each loop, while loop, do-while loop, Iterator, and ListIterator.

Conclusion

Array vs ArrayList: Understanding the differences and considering the trade-offs allows developers to make informed decisions when selecting the appropriate data structure for their programs.

Also Read : ArrayList vs LinkedList