What Is ArrayList in Data Structure?


Scott Campbell

The ArrayList is a fundamental data structure in programming that allows us to store and manipulate a collection of objects. It provides dynamic resizing, which means that it can grow or shrink as needed to accommodate the elements added or removed from it. In this article, we will explore the ArrayList in detail and understand its features and functionality.

Creating an ArrayList

To create an ArrayList in most programming languages, you need to import the necessary libraries or modules. Let’s take Java as an example.

First, you need to import the java.util package:

import java.util.ArrayList;

Next, you can declare and instantiate an ArrayList:

ArrayList names = new ArrayList<>();

In this example, we have created an ArrayList named “names” that can store strings. You can replace `String` with any other data type you want to store.

Adding Elements

To add elements to an ArrayList, you can use the `add()` method:


Now, our “names” ArrayList contains three elements: “John”, “Emma”, and “Michael”.

Accessing Elements

You can access elements in an ArrayList by their index using square brackets (`[]`). The index starts from 0 for the first element:

String firstName = names.get(0);
System.out.println(firstName); // Output: John

In this example, we accessed the first element (“John”) using the `get()` method.

Removing Elements

To remove elements from an ArrayList, you can use the `remove()` method:


This line of code removes the element at index 1 (in this case, “Emma”) from the ArrayList.

ArrayList Size

You can get the size of an ArrayList using the `size()` method:

int size = names.size();
System.println(size); // Output: 2

In this example, we retrieved the number of elements in the “names” ArrayList, which is 2 after removing one element.

Iterating over an ArrayList

You can use a loop to iterate over all the elements in an ArrayList. Let’s see an example using a for-each loop:

for (String name : names) {

This loop will print each element in the “names” ArrayList on a new line.


The ArrayList is a versatile and powerful data structure that allows us to store and manipulate collections of objects. It provides dynamic resizing, making it flexible for various programming needs.

We have explored its creation, adding and removing elements, accessing elements by index, retrieving the size, and iterating over its contents. With this knowledge, you can now leverage the ArrayList in your programming projects to organize and manage collections efficiently.

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