Is it possible to create in Java 8 a unlimitedly growing in lazy way collection, defined by recursion?

Question

I can create a recursive closure:

static IntUnaryOperator fibo;
fibo = 
    (i) -> 
    i<2 ? 1 : fibo.applyAsInt(i-1)+ fibo.applyAsInt(i-2);
         


        

Answer 1

I cannot think up a good general solution, but if you want to access specifically two previous elements, this could be done in quite easy way defining the custom Spliterator like this:

public static IntStream iterate(int first, int second, IntBinaryOperator generator) {
    Spliterator.OfInt spliterator = new AbstractIntSpliterator(Long.MAX_VALUE, 
                                             Spliterator.ORDERED) {
        int prev1 = first, prev2 = second;
        int pos = 0;

        @Override
        public boolean tryAdvance(IntConsumer action) {
            if(pos < 2) {
                action.accept(++pos == 1 ? prev1 : prev2);
            } else {
                int next = generator.applyAsInt(prev1, prev2);
                prev1 = prev2;
                prev2 = next;
                action.accept(next);
            }
            return true;
        }
    };
    return StreamSupport.intStream(spliterator, false);
}

Usage:

iterate(1, 1, Integer::sum).limit(20).forEach(System.out::println);