# How to create an ArrayList in Java

By Atta Ur Rehman Shah (https://attacomsian.com/about). Published Aug 10, 2019, updated Oct 8, 2022. Topics: Java.
Canonical URL: https://attacomsian.com/blog/how-to-create-an-arraylist-in-java

> A short guide to create and use ArrayList in Java.

The `ArrayList` class in Java is a widely used data structure for storing dynamic data. It implements the `List` interface, a part of Java's `Collection` framework. The developers favor `ArrayList` over the normal array because of its flexibility to dynamically grow and shrink.

## `ArrayList` vs. Array

There are five notable differences between an `ArrayList` and an array in Java:

1. Unlike an array that has a fixed length, `ArrayList` is resizable. When a new element is added, it is extended automatically. Likewise, when an element is removed, it shrinks. There are no empty slots.
2. `ArrayList` uses an array internally to store the elements. So you can use the zero-based index to randomly retrieve the elements.
3. Just like the array, you can store duplicate and null values in `ArrayList`.
4. `ArrayList` maintains the insertion order of the elements.
5. Unlike the array that can be of primitive type, you cannot use primitives like `int`, `double`, and `char` to create an `ArrayList`.  You must use reference types like `String`, `Integer`, or `Double` to create an `ArrayList`.

## Creating an `ArrayList`

There are multiple ways to create an `ArrayList`:

```java
// create an empty array list
List<String> list = new ArrayList<>();

// create and initialize array list
List<String> list2 = new ArrayList<>(Arrays.asList("?", "?", "?", "?"));

// create an array list with a specified initial size
List<String> list3 = new ArrayList<>(10);

// Java 8 `Arrays.asList()` method (immutable)
List<Integer> list4 = Arrays.asList(1, 2, 3, 4, 5);

// Java 9 `List.of()` method (immutable)
List<Integer> list5 = List.of(1, 2, 3, 4, 5);
```

## `ArrayList` Methods

The `ArrayList` class also inherits methods from parent classes `List`, `Collection`, and `Iterable`. The most popular methods are `set()`, `get()`, `size()`, `remove()`, and `isEmpty()`. Here is a simple example of an `ArrayList` showing the use of these methods: 

```java
List<String> list = new ArrayList<>();

// add elments
list.add("?");
list.add("?");
list.add("?");
list.add("?");

// get items
list.get(0); // ? 
list.get(2); // ?
        
// get elements count
list.size(); // 4

// update element at index 1
list.set(1, "?"); 
list.get(1); // ?

// remove elements using value
list.remove("?"); // true

// remove elements using the index
list.remove(0); // true

// check if list is empty
list.isEmpty(); // false
```

## Iterating over `ArrayList`

You can iterate over the `ArrayList` elements through multiple methods:

```javascript
// simple `for` loop
for (int i = 0; i < foods.size(); i++) {
    System.out.println(foods.get(i));
}

// for each loop
for (String item : foods) {
    System.out.println(item);
}

// Java 8 `forEach` from Streams API
foods.forEach(System.out::println);
```