Java int[] array to HashSet<Integer>

I have an array of int:

int[] a = {1, 2, 3};

I need a typed set from it:

Set<Integer> s;

If I do the following:

s = new HashSet(Arrays.asList(a));

it, of course, thinks I mean:

List<int[]>

whereas I meant:

List<Integer>

This is because int is a primitive. If I had used String, all would work:

Set<String> s = new HashSet<String>(
    Arrays.asList(new String[] { "1", "2", "3" }));

How to easily, correctly and succinctly go from:

A) int[] a...

to

B) Integer[] a ...

Thanks!

Using Stream:

// int[] nums = {1,2,3,4,5}
Set<Integer> set = Arrays.stream(nums).boxed().collect(Collectors.toSet())

The question asks two separate questions: converting int[] to Integer[] and creating a HashSet<Integer> from an int[]. Both are easy to do with Java 8 streams:

int[] array = ...
Integer[] boxedArray = IntStream.of(array).boxed().toArray(Integer[]::new);
Set<Integer> set = IntStream.of(array).boxed().collect(Collectors.toSet());
//or if you need a HashSet specifically
HashSet<Integer> hashset = IntStream.of(array).boxed()
    .collect(Collectors.toCollection(HashSet::new));

Some further explanation. The asList method has this signature

public static <T> List<T> asList(T... a)

So if you do this:

List<Integer> list = Arrays.asList(1, 2, 3, 4)

or this:

List<Integer> list = Arrays.asList(new Integer[] { 1, 2, 3, 4 })

In these cases, I believe java is able to infer that you want a List back, so it fills in the type parameter, which means it expects Integer parameters to the method call. Since it's able to autobox the values from int to Integer, it's fine.

However, this will not work

List<Integer> list = Arrays.asList(new int[] { 1, 2, 3, 4} )

because primitive to wrapper coercion (ie. int[] to Integer[]) is not built into the language (not sure why they didn't do this, but they didn't).

As a result, each primitive type would have to be handled as it's own overloaded method, which is what the commons package does. ie.

public static List<Integer> asList(int i...);

Or you could easly use Guava to convert int[] to List<Integer>:

Ints.asList(int...)

asList

public static List<Integer> asList(int... backingArray)

Returns a fixed-size list backed by the specified array, similar to Arrays.asList(Object[]). The list supports List.set(int, Object), but any attempt to set a value to null will result in a NullPointerException.

The returned list maintains the values, but not the identities, of Integer objects written to or read from it. For example, whether list.get(0) == list.get(0) is true for the returned list is unspecified.

You can use ArrayUtils in Apache Commons:

int[] intArray  = { 1, 2, 3 };
Integer[] integerArray = ArrayUtils.toObject(intArray);