Either.java

/**
 * I know Either is a well known class in Scala, but I'm wondering if I've stumbled onto a well known pattern with this
 * extract() function?
 */
     public static final class Either<A,B> {
        private final A left;
        private final B right;

        public boolean ifLeft(@Nonnull Consumer<A> todo){
            if (left != null) {
                todo.accept(left);
                return true;
            }
            return false;
        }

        public boolean ifRight(@Nonnull Consumer<B> todo) {
            if (right != null) {
                todo.accept(right);
                return true;
            }
            return false;
        }

        public <C> C extract(@Nonnull Function<A,C> extractLeft, @Nonnull Function<B,C> extractRight) {
            if (left != null) {
                return extractLeft.apply(left);
            }
            return extractRight.apply(right);
        }

        static <X> Either<X, ?> left(@Nonnull X a) {
            return new Either<>(a, null);
        }

        static <Y> Either<?, Y> right(@Nonnull Y b) {
            return new Either<>(null, b);
        }

        /** use static factories left() and right() */
        private Either(A a, B b) {
            this.left = a;
            this.right = b;
        }
    }