Convert Between Array of Primitives and Array of Objects

Learn to convert an array of primitives (int, long or double) to an array of objects (Integer, Double or Long), and vice versa. For example, we will convert int[] to Integer[] and then convert back the Integer[] to int[].

Note that all the techniques follow the same logic for the conversion process i.e. iterate over the existing array, convert the current item to object (or primitive) and add to the new array. The APIs discussed below add the syntactic sugar to make the code more readable.

1. Converting using the Stream API

We need to use the Stream.toArray() method that returns an array containing the items from a given stream. We need to convert the item type before collecting it into the new array.

1.1. Primitive Array to Object Array

Java program to convert the int[] to Integer[]. Note that, by default, toArray() method returns the Object[] so specifying the generator function Integer[]::new is important.

int[] primitiveArray = new int[]{0, 1, 2, 3, 4, 5};

Integer[] outputArray = Arrays.stream(primitiveArray)
        .boxed()
        .toArray(Integer[]::new);

1.2. Object Array to Primitive Array

Java program to convert the Integer[] to int[]. To convert the Integer object to int value, we are using the stream.mapToInt() function. This method returns an IntStream consisting of the int values corresponding to the Integer objects in the array.

If there are null items in the array then this method will throw NullPointerException.

Integer[] objectArray = new Integer[]{0, 1, 2, 3, 4, 5};

int[] outputArray = Arrays.stream(objectArray)
        .mapToInt(Integer::intValue)
        .toArray();

2. Converting using Apache Common’s ArrayUtils

The ArrayUtils class has many static utility methods to perform common tasks in a single statement. It improves the code readability and thus it is easy to maintain such code.

Bothe methods internally use the for-loop for iterating over the original array and populating the new array, so performance-wise you will see much difference as compared to using the Stream API.

Find the latest version of Common’s Lang in the Maven repo.

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.12.0</version>
</dependency>

2.1. Primitive Array to Object Array

The ArrayUtils.toObject() method converts an array of primitives to an array of objects. The method returns null for a null input array.

int[] primitiveArray = new int[]{0, 1, 2, 3, 4, 5};

Integer[] outputArray = ArrayUtils.toObject(primitiveArray);

2.2. Object Array to Primitive Array

The ArrayUtils.toPrimitive() method converts an array of objects to an array of corresponding primitives. This method throws NullPointerException if array content is null.

Integer[] objectArray = new Integer[]{0, 1, 2, 3, 4, 5};

int[] outputArray = ArrayUtils.toPrimitive(objectArray);

3. Conclusion

In this simple Java tutorial, we learned to convert primitive arrays to object arrays, and converted object arrays to primitive arrays. We learned to use the Java Streams API and Apache Common’s ArrayUtils class for it.

Both techniques will

Happy Learning !!

Sourcecode on Github