How to create a int[] or a Collection<Integer> with the value 0,1,2,...,N in one line in Java using lambda expression?

Question

I would like to do something like this:

int[] seq = new int[N];
for (int i = 0 ; i < N ; i++) {
    seq[i] = i;
}

...in one line, and i am wondering if it is possible with lambda expression.

If it works with ArrayList<Integer>, it is okay for me.

Answer 1

Starting from Java 9 you can use the three-argument IntStream.iterate:

int[] seq = IntStream.iterate(0, x -> x < N, x -> x + 1).toArray();

Where:

IntStream.iterate​(int seed, IntPredicate hasNext, IntUnaryOperator next):

• seed - the initial element;
• hasNext - a predicate to apply to elements to determine when the stream must terminate;
• next - a function to be applied to the previous element to produce a new element.