Question

I’m looking for a Google Collections method that returns the first result of a sequence of Suppliers that doesn’t return null.

I was looking at using Iterables.find() but in my Predicate I would have to call my supplier to compare the result against null, and then have to call it again once the find method returned the supplier.

Answer 1

Given your comment to Calm Storm’s answer (the desire not to call Supplier.get() twice), then what about:

private static final Function<Supplier<X>, X> SUPPLY = new Function<....>() {
    public X apply(Supplier<X> in) {
        // If you will never have a null Supplier, you can skip the test;
        // otherwise, null Supplier will be treated same as one that returns null
        // from get(), i.e. skipped
        return (in == null) ? null : in.get();
    }
}

then

Iterable<Supplier<X>> suppliers = ... wherever this comes from ...

Iterable<X> supplied = Iterables.transform(suppliers, SUPPLY);

X first = Iterables.find(supplied, Predicates.notNull());

note that the Iterable that comes out of Iterables.transform() is lazily-evaluated, therefore as Iterables.find() loops over it, you only evaluate as far as the first non-null-returning one, and that only once.