ArrayList

ArrayList

Written by: David Hancu

Reading Time: 3 minutes

Introduction

Hello everyone and welcome to a new article here on JavaChallenges. In this article, we will focus on ArrayList, a very useful class in most projects. So without any waste of time, let's get right into it.

What is the ArrayList class?

The ArrayList class is a nice class that is part of the java.util package. It is a combination of the arrays and lists, making something often used in code. If you ever used arrays, you will know that it is impossible to change the size of the array because it is defined when you create it. However, lists don't have this problem. You define the list, and then you can use the add() method to add more values or remove() to remove. The key difference is that creating a list is made without defining a size.

This is the standard array declaration:

String[] array = new String[size];

But you can define an ArrayList like this:

ArrayList<String> list = new ArrayList<>();

You can see the clear advantage of the ArrayList in this comparison.

Specific Information

The ArrayList provides some pretty neat features:

• It allows duplicate elements.
• The elements maintain their insertion order.
• You can access it at random points by using indexes.

Use Examples

You can find one use-case for this useful class in our first beginner challenge, which can be found here. Other than that, we collected some of the most used examples.

Defining an ArrayList

In this example, we will consider T the type of elements that will be held by this list. The type can be Boolean, String, etc.

ArrayList<T> list = new ArrayList<>();

Adding Elements

In this example, we will consider T the type of elements that will be held by this list. The type can be Boolean, String, etc.

ArrayList<T> list = new ArrayList<>();
list.add(element);

Removing Elements

In this example, we will consider T the type of elements that will be held by this list. The type can be Boolean, String, etc.

ArrayList<T> list = new ArrayList<>();
list.remove(element); // Alternatively, you can use the index of the element.

Iterating over the elements

In this example, we will consider T the type of elements that will be held by this list. The type can be Boolean, String, etc.

ArrayList<T> list = new ArrayList<>();
for(T element : list)
{
    // you can use the element!
}

Accessing elements

In this example, we will consider T the type of elements that will be held by this list. The type can be Boolean, String, etc.

ArrayList<T> list = new ArrayList<>();
list.get(index);

Checking if the list contains an element

In this example, we will consider T the type of the elements that will be held by this list. The type can be Boolean, String, etc.

ArrayList<T> list = new ArrayList<>();
boolean contains = list.contains(element);

Ending

Thank you for reading this article on the ArrayList class. I hope I helped you with finding out more about this class. I'm David and this is JavaChallenges. Have a nice day and remember: coding is fun and Google is your friend :).