CODEWITHSUNDEEP
javaarraysjava-streamhashset
user63898
user63898

Reputation: 30925

Java failed to convert int array to Set using Collectors.toSet()

I can't understand the basic thing I have here:

 int[] arr = {2,5,2,4,6,6,1,5,4};
        Set<Integer> orederSet  = new HashSet<Integer>(Arrays.stream(arr).collect(Collectors.toSet()));

Side note: also this not working:

Set<Integer> orederSet  = new HashSet<Integer>(Arrays.asList(arr));

which gives me compile error:

java: method collect in interface java.util.stream.IntStream cannot be applied to given types;
  required: java.util.function.Supplier<R>,java.util.function.ObjIntConsumer<R>,java.util.function.BiConsumer<R,R>
  found: java.util.stream.Collector<java.lang.Object,capture#1 of ?,java.util.Set<java.lang.Object>>
  reason: cannot infer type-variable(s) R
    (actual and formal argument lists differ in length)

What is wrong in my code?

Upvotes: 0

Views: 725

Answers (2)

Slaw
Slaw

Reputation: 46181

Your arr is an int[]. That means you're calling Arrays#stream(int[]), which returns an IntStream. But none of the primitive stream interfaces1 have a #collect(Collector) method. You have to convert the IntStream into a Stream<Integer>. The easiest way to do that is with the IntStream#boxed() method.

int[] arr = {2, 5, 2, 4, 6, 6, 1, 5, 4};

Set<Integer> set =
        Arrays.stream(arr)                  // IntStream
              .boxed()                      // Stream<Integer>
              .collect(Collectors.toSet()); // Set<Integer>

As for why the following doesn't work:

Set<Integer> set = new HashSet<>(Arrays.asList(arr));

That's due to Arrays.asList(arr) returning a List<int[]> rather than a List<Integer>.

Neither primitives nor arrays work especially well with generics. Arrays of primitives are worse. A primitive can at least be auto-boxed to the reference type (and vice versa, i.e., unboxed) when appropriate. But primitive arrays have no such special treatment.

1. The primitive stream interfaces include IntStream, LongStream, and DoubleStream.

Upvotes: 3

pitpet
pitpet

Reputation: 21

Try to convert IntStream:

Set<Integer> orderSet = Arrays.stream(arr).boxed().collect(Collectors.toSet());

Upvotes: 2

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