Java Utililty Methods Iterable Size

if (pairs instanceof List) {
    return ((List<?>) pairs).size();
} else {
    throw new IllegalArgumentException("Cannot determine split size from split result.");

if (iterable instanceof Collection<?>) {
    return ((Collection<?>) iterable).size();
} else {
    Iterator<?> it = iterable.iterator();
    int i = 0;
    while (it.hasNext()) {
        i++;
    return i;

if (!it.iterator().hasNext())
    return null;
final Iterator<T> iterator = it.iterator();
T o = iterator.next();
if (iterator.hasNext())
    throw new IllegalStateException("Found multiple items in iterator over " + o.getClass().getName());
return o;

if (coll == null)
    return null;
Iterator<T> iterator = coll.iterator();
T firstElement = iterator.next();
return iterator.hasNext() ? null : firstElement;

if (iterable == null)
    return null;
final Iterator<? extends T> iter = iterable.iterator();
if (!iter.hasNext())
    return null;
final T result = iter.next();
if (iter.hasNext()) {
    throw new IllegalArgumentException("More than (expected) one element in " + iterable);
...

return getSingleOrNull(iterable.iterator());

int result = 0;
for (Object eleme : iterable) {
    result++;
return result;

int size = 0;
for (Iterator<E> iter = itrbl.iterator(); iter.hasNext();) {
    iter.next();
    size++;
return size;

Iterator<E> it = itrbl.iterator();
for (int i = 0; i < k; i++) {
    if (!it.hasNext())
        return false;
    it.next();
return !it.hasNext();

Iterator<T> i = iterable.iterator();
if (i.hasNext()) {
    return i.next();
return null;