Java How to Convert ArrayList to Array Easily

Use arrayList.toArray(new Type[arrayList.size()]) to convert an ArrayList to an array in Java, for example: String[] arr = list.toArray(new String[list.size()]).

Examples

Input["apple", "banana", "cherry"]

Output["apple", "banana", "cherry"]

Input[]

Output[]

Input["one"]

Output["one"]

How to Think About It

To convert an ArrayList to an array, you create a new array of the same type and size, then use the ArrayList's toArray method to fill it. This method copies all elements from the list into the new array.

Algorithm

1

Create an ArrayList with elements.

2

Create a new array of the same type and size as the ArrayList.

3

Call the ArrayList's <code>toArray</code> method with the new array as argument.

4

The method fills the array with the list's elements and returns it.

5

Use or print the resulting array.

Code

java

import java.util.ArrayList;
import java.util.Arrays;

public class ConvertArrayList {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("apple");
        list.add("banana");
        list.add("cherry");

        String[] array = list.toArray(new String[list.size()]);
        System.out.println(Arrays.toString(array));
    }
}

Output

[apple, banana, cherry]

Dry Run

Let's trace converting ["apple", "banana", "cherry"] from ArrayList to array.

1

Create ArrayList

list = ["apple", "banana", "cherry"]

2

Create new array

new String[3] -> [null, null, null]

3

Call toArray

array = list.toArray(new String[3]) -> ["apple", "banana", "cherry"]

Step	Array Contents
Before toArray	[null, null, null]
After toArray	["apple", "banana", "cherry"]

Why This Works

Step 1: Why create a new array?

The toArray method needs an array to fill, so you create one with the same size and type as the ArrayList.

Step 2: How does toArray work?

It copies each element from the ArrayList into the new array in order.

Step 3: Resulting array

The returned array contains all elements from the list and can be used like any normal array.

Alternative Approaches

Using toArray() without argument

java

import java.util.ArrayList;
import java.util.Arrays;

public class ConvertArrayListAlt {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("apple");
        list.add("banana");
        list.add("cherry");

        Object[] array = list.toArray();
        System.out.println(Arrays.toString(array));
    }
}

Returns an Object array, so you may need to cast elements later.

Using Java 8 Streams

java

import java.util.ArrayList;
import java.util.List;

public class ConvertArrayListStream {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("apple");
        list.add("banana");
        list.add("cherry");

        String[] array = list.stream().toArray(String[]::new);
        for (String s : array) {
            System.out.print(s + " ");
        }
    }
}

Uses streams to convert, more flexible but slightly more complex.

Complexity: O(n) time, O(n) space

Time Complexity

The method copies each element once, so time grows linearly with the number of elements.

Space Complexity

A new array of the same size is created, so space usage is proportional to the list size.

Which Approach is Fastest?

Using toArray(new Type[size]) is efficient and type-safe; streams add overhead but offer flexibility.

Approach	Time	Space	Best For
toArray(new Type[size])	O(n)	O(n)	Simple, type-safe conversion
toArray()	O(n)	O(n)	Quick but returns Object[] needing casting
Streams toArray	O(n)	O(n)	Flexible, functional style