Convert Java Array to Iterable

I have an Array of primitives, for example for int, int[] foo. It might be a small sized one, or not.

int foo[] = {1,2,3,4,5,6,7,8,9,0};

What is the best way to create an Iterable<Integer> from it?

Iterable<Integer> fooBar = convert(foo);

Notes:

Please do not answer using loops (unless you can give a good explanation on how the compiler do something smart about them?)

Also note that

int a[] = {1,2,3};
List<Integer> l = Arrays.asList(a);

Will not even compile

Type mismatch: cannot convert from List<int[]> to List<Integer>

Also check Why is an array not assignable to Iterable? before answering.

Also, if you use some library (e.g., Guava), please explain why this is the Best. ( Because its from Google is not a complete answer :P )

Last, since there seems to be a homework about that, avoid posting homeworkish code.

Solution 1:

Integer foo[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };

List<Integer> list = Arrays.asList(foo);
// or
Iterable<Integer> iterable = Arrays.asList(foo);

Though you need to use an Integer array (not an int array) for this to work.

For primitives, you can use guava:

Iterable<Integer> fooBar = Ints.asList(foo);

<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>15.0</version>
    <type>jar</type>
</dependency>

For Java8 with lambdas: (Inspired by Jin Kwon's answer)

final int[] arr = { 1, 2, 3 };
final Iterable<Integer> i1 = () -> Arrays.stream(arr).iterator();
final Iterable<Integer> i2 = () -> IntStream.of(arr).iterator();
final Iterable<Integer> i3 = () -> IntStream.of(arr).boxed().iterator();

Solution 2:

just my 2 cents:

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

java.lang.Iterable<Integer> aIterable=new Iterable<Integer>() {

    public Iterator<Integer> iterator() {
       return new Iterator<Integer>() {
            private int pos=0;

            public boolean hasNext() {
               return a.length>pos;
            }

            public Integer next() {
               return a[pos++];
            }

            public void remove() {
                throw new UnsupportedOperationException("Cannot remove an element of an array.");
            }
        };
    }
};

Solution 3:

With Java 8, you can do this.

final int[] arr = {1, 2, 3};
final PrimitiveIterator.OfInt i1 = Arrays.stream(arr).iterator();
final PrimitiveIterator.OfInt i2 = IntStream.of(arr).iterator();
final Iterator<Integer> i3 = IntStream.of(arr).boxed().iterator();

Solution 4:

Guava provides the adapter you want as Int.asList(). There is an equivalent for each primitive type in the associated class, e.g., Booleans for boolean, etc.

int foo[] = {1,2,3,4,5,6,7,8,9,0};
Iterable<Integer> fooBar = Ints.asList(foo);
for(Integer i : fooBar) {
    System.out.println(i);
}

The suggestions above to use Arrays.asList won't work, even if they compile because you get an Iterator<int[]> rather than Iterator<Integer>. What happens is that rather than creating a list backed by your array, you created a 1-element list of arrays, containing your array.