为什么guava joiner实现了一个私有方法iterable（final Object first，final Object second，final Object [] rest）？

private static Iterable<Object> iterable(
        final Object first, final Object second, final Object[] rest) {
    checkNotNull(rest);
    return new AbstractList<Object>() {
        @Override
        public int size() {
            return rest.length + 2;
        }

        @Override
        public Object get(int index) {
            switch (index) {
                case 0:
                    return first;
                case 1:
                    return second;
                default:
                    return rest[index - 2];
            }
        }
    };
}
private static Iterable<Object> iterable(