android/guava/src/com/google/common/collect/Maps.java
@Beta
  @GwtIncompatible // NavigableMap
  public static <K extends Comparable<? super K>, V> NavigableMap<K, V> subMap(
      NavigableMap<K, V> map, Range<K> range) {
    if (map.comparator() != null
        && map.comparator() != Ordering.natural()
        && range.hasLowerBound()
        && range.hasUpperBound()) {
      checkArgument(
          map.comparator().compare(range.lowerEndpoint(), range.upperEndpoint()) <= 0,
          "map is using a custom comparator which is inconsistent with the natural ordering.");
    }
    if (range.hasLowerBound() && range.hasUpperBound()) {
      return map.subMap(
          range.lowerEndpoint(),
          range.lowerBoundType() == BoundType.CLOSED,
          range.upperEndpoint(),
          range.upperBoundType() == BoundType.CLOSED);
    } else if (range.hasLowerBound()) {
      return map.tailMap(range.lowerEndpoint(), range.lowerBoundType() == BoundType.CLOSED);
    } else if (range.hasUpperBound()) {
      return map.headMap(range.upperEndpoint(), range.upperBoundType() == BoundType.CLOSED);
    }
    return checkNotNull(map);
  }
@Beta
  @GwtIncompatible // NavigableMap
  public static <K extends Comparable<? super K>, V> NavigableMap<K, V> subMap(
      NavigableMap<K, V> map, Range<K> range) {
    if (map.comparator() != null
        && map.comparator() != Ordering.natural()
        && range.hasLowerBound()
        && range.hasUpperBound()) {
      checkArgument(
          map.comparator().compare(range.lowerEndpoint(), range.upperEndpoint()) <= 0,
          "map is using a custom comparator which is inconsistent with the natural ordering.");
    }
    if (range.hasLowerBound() && range.hasUpperBound()) {
      return map.subMap(
          range.lowerEndpoint(),
          range.lowerBoundType() == BoundType.CLOSED,
          range.upperEndpoint(),
          range.upperBoundType() == BoundType.CLOSED);
    } else if (range.hasLowerBound()) {
      return map.tailMap(range.lowerEndpoint(), range.lowerBoundType() == BoundType.CLOSED);
    } else if (range.hasUpperBound()) {
      return map.headMap(range.upperEndpoint(), range.upperBoundType() == BoundType.CLOSED);
    }
    return checkNotNull(map);
  }
Returns a view of the portion of {@code map} whose keys are contained by {@code range}.

<p>This method delegates to the appropriate methods of {@link NavigableMap} (namely {@link
NavigableMap#subMap(Object, boolean, Object, boolean) subMap()}, {@link
NavigableMap#tailMap(Object, boolean) tailMap()}, and {@link NavigableMap#headMap(Object,
boolean) headMap()}) to actually construct the view. Consult these methods for a full
description of the returned view's behavior.

<p><b>Warning:</b> {@code Range}s always represent a range of values using the values' natural
ordering. {@code NavigableMap} on the other hand can specify a custom ordering via a {@link
Comparator}, which can violate the natural ordering. Using this method (or in general using
{@code Range}) with unnaturally-ordered maps can lead to unexpected and undefined behavior.

@since 20.0