How to convert ArrayList to Array In Java?

In this article, we will see how to convert an ArrayList to Array in Java.

Introduction

ArrayList in Java is an ordered collection. Also ArrayList allows the duplicate elements.

We have see the ArrayList method like add(), addAll(), remove(), set(), iterate(), clear() and contains().

ArrayList mostly provides all the regular operations that needs to be perform on Array. So convert ArrayList to Array only when your use-case requires it.

We can convert an ArrayList to Array in Java using the toArray() method.

There are two methods to convert an ArrayList to Array. They are as given below.

1. public Object[] toArray() method
2. public <T> T[] toArray(T[] a) method

Lets see both methods one by one.

1. public Object[] toArray() method

toArray() method returns an array containing all of the elements in this ArrayList in proper sequence.

The method signature is given below.

1
public Object[] toArray()

As shown in the above method signature, the return type of this method is Object[]. It returns an array that contains all the elements of the ArrayList in proper sequence.

I have given an example java program to convert an ArrayList to Array. It converts an ArrayList of String to Object Array i.e Object [].

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/**
 * A java program to convert an ArrayList to array using
 * toArray method.
 * 
 * toArray() method returns Object[]
 * 
 * @author Gaurav Kukade at coderolls.com
 *
 */
public class ArrayListToArray {

	public static void main(String[] args) {
		ArrayList<String> arrayList = new ArrayList<String>();
		
		//adding elements to the arrayList
		arrayList.add("Meta");
		arrayList.add("Apple");
		arrayList.add("Amazon");
		arrayList.add("Netflix");
		arrayList.add("Microsoft");
		arrayList.add("Google");
		
		System.out.println("ArrayList: \n"+ arrayList);
		
		// convert ArrayList to array
		Object[] objects = arrayList.toArray();
		
		System.out.println("\nArray:");
		
		//we will receive the object array, so iterate on it to print each element
		for(Object obj:objects) {
			System.out.println(obj);
		}
	}
}

Output:

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ArrayList: 
[Meta, Apple, Amazon, Netflix, Microsoft, Google]

Array:
Meta
Apple
Amazon
Netflix
Microsoft
Google

2. public <T> T[] toArray(T[] a) method

This method also returns an array that contains all the elements of the ArrayList in proper sequence.

The method signature is as given below.

1
public <T> T[] toArray(T[] a)

As shown in the method signature, this method accepts one parameter.

• T[] a:- An new array of type T, into which the elements of the list are to be stored. If the specified array is not enough to store all the elements of the ArrayList, a new array of the same type will be created.

This method returns T [] i.e. An array of the specified type can be returned.

I have given a sample java program to convert an ArrayList to array. Here, we will be converting an ArrayList of type String to String Array i.e String [].

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import java.util.ArrayList;

/**
 * A java program to convert an ArrayList to array using
 * toArray method.
 * 
 * toArray(T[] a) method returns T[]
 * 
 * @author Gaurav Kukade at coderolls.com
 *
 */
public class ArrayListToArray2 {

	public static void main(String[] args) {
		ArrayList<String> arrayList = new ArrayList<String>();
		
		//adding elements to the arrayList
		arrayList.add("Meta");
		arrayList.add("Apple");
		arrayList.add("Amazon");
		arrayList.add("Netflix");
		arrayList.add("Microsoft");
		arrayList.add("Google");
		
		System.out.println("ArrayList: \n"+ arrayList);
		
		// convert ArrayList to array
		// pass a new String array of the arrayList size as a param to toArray
		//String[] elements = arrayList.toArray(new String[arrayList.size()]);
		
		//kindly read the 'Important Note' below
		String[] elements = arrayList.toArray(new String[0]);

		
		System.out.println("\nArray:");
		//we will receive the string array, so iterate on it to print each element
		for(String str:elements) {
			System.out.println(str);
		}
	}
}

Output:

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ArrayList: 
[Meta, Apple, Amazon, Netflix, Microsoft, Google]

Array:
Meta
Apple
Amazon
Netflix
Microsoft
Google

Important Note:

The code above used new String[arrayList.size()] as a paramter to a toArray() method. However, this blogpost from Aleksey Shipilёv reveals that due to JVM optimizations, using new String[0] is better now.

Conclusion

We can convert an ArrayList to Array in Java using the toArray() method.

There are two versions of the toArray() method.

1. public Object[] toArray() method
2. public <T> T[] toArray(T[] a) method

The example java programs given in the above tutorial can be found at this GitHub Repository.

Please write you thoughts in the comment section below.