Converting Array of Primitives to Array of Containers in Java

You have to loop through your array.

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Updated after @seanizer answer :

Basically the toObject(byte[] array) method will do the looping for you :

public static Byte[] toObject(byte[] array) {
    if (array == null) {
        return null;
    } else if (array.length == 0) {
        return EMPTY_BYTE_OBJECT_ARRAY;
    }
    final Byte[] result = new Byte[array.length];
    for (int i = 0; i < array.length; i++) {
        result[i] = new Byte(array[i]);
    }
    return result;
}

And unless you will really use the commons lang lib, you should simply reuse this method and avoid a useless dependency (IMHO).

Apache Commons

Apache Commons / Lang has a class ArrayUtils that defines these methods.

• All methods called toObject(...) convert from primitive array to wrapper array
• All called toPrimitive(...) convert from wrapper object array to primitive array

Example:

final int[]     original        = new int[] { 1, 2, 3 };
final Integer[] wrappers        = ArrayUtils.toObject(original);
final int[]     primitivesAgain = ArrayUtils.toPrimitive(wrappers);
assert Arrays.equals(original, primitivesAgain);

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Guava

But then I'd say that Arrays of wrapped primitives are not very useful, so you might want to have a look at Guava instead, which provides Lists of all numeric types, backed by primitive arrays:

List<Integer> intList = Ints.asList(1,2,3,4,5);
List<Long> longList   = Longs.asList(1L,2L,3L,4L,5L);
// etc.

The nice think about these array-backed collections is that

1. they are live views (i.e. updates to the array change the list and vice-versa)
2. the wrapper objects are only created when needed (e.g. when iterating the List)

See: Guava Explained / Primitives

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Java 8

On the other hand, with Java 8 lambdas / streams, you can make these conversions pretty simple without using external libraries:

int[] primitiveInts = {1, 2, 3};
Integer[] wrappedInts = Arrays.stream(primitiveInts)
                              .boxed()
                              .toArray(Integer[]::new);
int[] unwrappedInts = Arrays.stream(wrappedInts)
                             .mapToInt(Integer::intValue)
                             .toArray();
assertArrayEquals(primitiveInts, unwrappedInts);

double[] primitiveDoubles = {1.1d, 2.2d, 3.3d};
Double[] wrappedDoubles = Arrays.stream(primitiveDoubles)
                                .boxed()
                                .toArray(Double[]::new);
double[] unwrappedDoubles = Arrays.stream(wrappedDoubles)
                                  .mapToDouble(Double::doubleValue)
                                  .toArray();

assertArrayEquals(primitiveDoubles, unwrappedDoubles, 0.0001d);

Note that the Java 8 version works for int, long and double, but not for byte, as Arrays.stream() only has overloads for int[], long[], double[] or a generic object T[].