Java ArrayList toArray() method
Syntax and Examples

Introduction

Sometimes you need to work with a standard Java array instead of an ArrayList. The `toArray()` method provides a simple and efficient way to convert your ArrayList into an array of the same type.

Syntax

    
public Object[] toArray()

public <T> T[] toArray(T[] a)
    
  

Parameters Table

Parameter	Description
a (for toArray(T[] a))	An array of the desired type. If the array is smaller than the ArrayList's size, it will be truncated; otherwise, it will be filled with null values. This serves as an initial array for the conversion.

Return Value

The toArray() method returns a new array containing all of the elements in the ArrayList in the order they are returned by the iterator.

Examples

Example 1: Converting to an Object Array

This example demonstrates how to convert an ArrayList of String objects into a standard Object[] array. This is useful when you need a generic array format.

    
import java.util.ArrayList;

public class ToArrayExample1 {
    public static void main(String[] args) {
        ArrayList<String> names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");

        Object[] nameArray = names.toArray();

        for (Object name : nameArray) {
            System.out.println(name);
        }
    }
}
    
  

Alice
Bob
Charlie

Explanation: The toArray() method without any arguments converts the ArrayList<String> names into an Object[] nameArray. The loop then iterates through the array and prints each element.

Example 2: Converting to a String Array

This example shows how to convert an ArrayList of String objects directly into a String[] array using the type-safe overload of toArray(). This avoids casting and is generally preferred.

    
import java.util.ArrayList;

public class ToArrayExample2 {
    public static void main(String[] args) {
        ArrayList<String> names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");

        String[] nameArray = names.toArray(new String[0]);

        for (String name : nameArray) {
            System.out.println(name);
        }
    }
}
    
  

Alice
Bob
Charlie

Explanation: The toArray(new String[0]) method converts the ArrayList<String> names into a String[] nameArray. Note that we pass an empty String array as an argument. This allows the ArrayList to create a new array of the correct size, avoiding potential resizing issues.

Example 3: Using with a Pre-existing Array

This example demonstrates how to use an existing array and have it populated by the ArrayList’s elements. If the provided array is smaller than the ArrayList's size, only the first few elements of the ArrayList are copied.

    
import java.util.ArrayList;

public class ToArrayExample3 {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<>();
        numbers.add(1);
        numbers.add(2);
        numbers.add(3);
        numbers.add(4);

        Integer[] existingArray = new Integer[2]; // Smaller array

        Integer[] result = numbers.toArray(existingArray);

        for (Integer number : result) {
            System.out.println(number);
        }
    }
}
    
  

1
2

Explanation: The existingArray is provided as an argument to the toArray(existingArray) method. Since it's smaller than the ArrayList, only the first two elements (1 and 2) are copied into it. Notice that existingArray now contains [1, 2]. The returned array will be a new array containing the first two elements of numbers.

Example 4: Using with a Pre-existing Array - Larger than ArrayList

This example shows what happens when you pass an array that is larger than the list. The excess elements are filled with null values.

    
import java.util.ArrayList;

public class ToArrayExample4 {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<>();
        numbers.add(1);
        numbers.add(2);

        Integer[] existingArray = new Integer[5]; // Larger array

        Integer[] result = numbers.toArray(existingArray);

        for (Integer number : result) {
            System.out.println(number == null ? "null" : number);
        }
    }
}
    
  

1
2
null
null
null

Explanation: The existingArray is provided as an argument to the toArray(existingArray) method. Since it's larger than the ArrayList, only the first two elements (1 and 2) are copied into it. The remaining slots in existingArray are filled with null values.