Convert a Set to a primitive array

Question

I am using the following code to convert a Set to int[]

Set<Integer> common = new HashSet<Integer>();
int[] myArray = (int[]) common.toArray();

the I got the following error:

 error: incompatible types: Object[] cannot be converted to int[]

What would be the most clean way to do the conversion without adding element one by one using a for loop? Thanks!

Finally a well-formatted question with proper grammar on StackOverflow — Tilak Maddy, May 21 '16 at 14:44

score 8 · Answer 1 · answered May 21 '16 at 14:45

8

You usually do this:

Set<Integer> common = new HashSet<Integer>();
int[] myArray = common.stream().mapToInt(Integer::intValue).toArray();

answered May 21 '16 at 14:45

xehpuk

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dude, i want to learn about `::` operator where do i learn it form ? – Tilak Maddy May 21 '16 at 14:48
@TilakMadichetti This is called a "method reference". See e.g. here: https://docs.oracle.com/javase/tutorial/java/javaOO/methodreferences.html – xehpuk May 21 '16 at 14:50
so `intValue` is a method in the Integer class ? – Tilak Maddy May 21 '16 at 15:02
Correct: https://docs.oracle.com/javase/8/docs/api/java/lang/Integer.html#intValue-- – xehpuk May 21 '16 at 15:33

s7vr · Answer 2 · 2016-05-21T20:06:12.047

7

Set<Integer> common = new HashSet<>();
int[] values = Ints.toArray(common);

edited May 21 '16 at 20:06

answered May 21 '16 at 14:53

s7vr

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`Integer[] != int[]` – xehpuk May 21 '16 at 15:34
Changed now to use the Guava's helper library. – s7vr May 21 '16 at 20:07

score 2 · Answer 3 · edited May 21 '16 at 15:17

2

You cannot explicitly cast something into an array.

Do this:

Integer[] arr = new Integer[common.size()];
Iterator<Integer> iterator = common.iterator(); 
int i = 0;
while (iterator.hasNext()){
    arr[i++] = iterator.next();
}

edited May 21 '16 at 15:17

Tom

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answered May 21 '16 at 14:39

Tilak Maddy

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@tom why would the code not compile ? – Tilak Maddy May 21 '16 at 15:04
@tom now would it work ? – Tilak Maddy May 21 '16 at 15:07
@Tom Please edit my answer – Tilak Maddy May 21 '16 at 15:15
[What is a raw type and why shouldn't we use it?](http://stackoverflow.com/q/2770321) – Tom May 21 '16 at 15:17

Convert a Set to a primitive array

3 Answers3