android/guava/src/com/google/common/collect/ImmutableSortedMap.java
public static <K, V> ImmutableSortedMap<K, V> copyOf(
      Map<? extends K, ? extends V> map, Comparator<? super K> comparator) {
    return copyOfInternal(map, checkNotNull(comparator));
  }
public static <K, V> ImmutableSortedMap<K, V> copyOf(
      Map<? extends K, ? extends V> map, Comparator<? super K> comparator) {
    return copyOfInternal(map, checkNotNull(comparator));
  }
Returns an immutable map containing the same entries as {@code map}, with keys sorted by the
provided comparator.

<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 any key or value in {@code map} is null
@throws IllegalArgumentException if any two keys are equal according to the comparator