How to create an infinite Stream out of an Iterator?

Question

Looking at the following class I\'ve made:

public class FibonacciSupplier implements Iterator {
    private final IntPredicate hasNextPredicat         


        

Answer 1

To add another answer, perhaps AbstractSpliterator is a better choice, especially given the example code. Generate is inflexible as there is no [good] way to give a stop condition except by using limit. Limit only accepts a number of items rather than a predicate, so we have to know how many items we want to generate - which might not be possible, and what if the generator is a black box passed to us?

AbstractSpliterator is a halfway house between having to write a whole spliterator, and using Iterator/Iterable. AbstractSpliterator lacks just the tryAdvance method where we first check our predicate for being done, and if not pass the generated value to an action. Here's an example of a Fibonacci sequence using AbstractIntSpliterator:

public class Fibonacci {
    private static class FibonacciGenerator extends Spliterators.AbstractIntSpliterator
    {
        private IntPredicate hasNextPredicate;
        private int beforePrevious = 0;
        private int previous = 0;

        protected FibonacciGenerator(IntPredicate hasNextPredicate)
        {
            super(Long.MAX_VALUE, 0);
            this.hasNextPredicate = hasNextPredicate;
        }

        @Override
        public boolean tryAdvance(IntConsumer action)
        {
            if (action == null)
            {
                throw new NullPointerException();
            }

            int next = Math.max(1, beforePrevious + previous);
            beforePrevious = previous;
            previous = next;

            if (!hasNextPredicate.test(next))
            {
                return false;
            }

            action.accept(next);

            return true;
        }

        @Override
        public boolean tryAdvance(Consumer action)
        {
            if (action == null)
            {
                throw new NullPointerException();
            }

            int next = Math.max(1, beforePrevious + previous);
            beforePrevious = previous;
            previous = next;

            if (!hasNextPredicate.test(next))
            {
                return false;
            }

            action.accept(next);

            return true;
        }
    }

    public static void main(String args[])
    {
        Stream infiniteStream = StreamSupport.stream(
                new FibonacciGenerator(i -> true), false);

        Stream finiteStream = StreamSupport.stream(
                new FibonacciGenerator(i -> i < 100), false);

        // Print with a side-effect for the demo
        infiniteStream.limit(10).forEach(System.out::println);
        finiteStream.forEach(System.out::println);
    }
} 

For more details I've covered generators in Java 8 in my blog http://thecannycoder.wordpress.com/