guava/src/com/google/common/collect/ImmutableSortedMultiset.java
public static <E> ImmutableSortedMultiset<E> copyOf(
      Comparator<? super E> comparator, Iterable<? extends E> elements) {
    if (elements instanceof ImmutableSortedMultiset) {
      @SuppressWarnings("unchecked") // immutable collections are always safe for covariant casts
      ImmutableSortedMultiset<E> multiset = (ImmutableSortedMultiset<E>) elements;
      if (comparator.equals(multiset.comparator())) {
        if (multiset.isPartialView()) {
          return copyOfSortedEntries(comparator, multiset.entrySet().asList());
        } else {
          return multiset;
        }
      }
    }
    elements = Lists.newArrayList(elements); // defensive copy
    TreeMultiset<E> sortedCopy = TreeMultiset.create(checkNotNull(comparator));
    Iterables.addAll(sortedCopy, elements);
    return copyOfSortedEntries(comparator, sortedCopy.entrySet());
  }
public static <E> ImmutableSortedMultiset<E> copyOf(
      Comparator<? super E> comparator, Iterable<? extends E> elements) {
    if (elements instanceof ImmutableSortedMultiset) {
      @SuppressWarnings("unchecked") // immutable collections are always safe for covariant casts
      ImmutableSortedMultiset<E> multiset = (ImmutableSortedMultiset<E>) elements;
      if (comparator.equals(multiset.comparator())) {
        if (multiset.isPartialView()) {
          return copyOfSortedEntries(comparator, multiset.entrySet().asList());
        } else {
          return multiset;
        }
      }
    }
    elements = Lists.newArrayList(elements); // defensive copy
    TreeMultiset<E> sortedCopy = TreeMultiset.create(checkNotNull(comparator));
    Iterables.addAll(sortedCopy, elements);
    return copyOfSortedEntries(comparator, sortedCopy.entrySet());
  }
Returns an immutable sorted multiset containing the given elements sorted by the given {@code
Comparator}. This method iterates over {@code elements} at most once.

<p>Despite the method name, this method attempts to avoid actually copying the data when it is
safe to do so. The exact circumstances under which a copy will or will not be performed are
undocumented and subject to change.

@throws NullPointerException if {@code comparator} or any of {@code elements} is null