Method immutableEnumMap

guava/src/com/google/common/collect/Maps.java:133–158

Returns an immutable map instance containing the given entries. Internally, the returned map will be backed by an EnumMap. The iteration order of the returned map follows the enum's iteration order, not the order in which the elements appear in the given map. @param map the map to make

(
      Map<K, ? extends V> map)

   * @since 14.0
   */
  public static <K extends Enum<K>, V> ImmutableMap<K, V> immutableEnumMap(
      Map<K, ? extends V> map) {
    if (map instanceof ImmutableEnumMap) {
      @SuppressWarnings("unchecked") // safe covariant cast
      ImmutableEnumMap<K, V> result = (ImmutableEnumMap<K, V>) map;
      return result;
    }
    Iterator<? extends Entry<K, ? extends V>> entryItr = map.entrySet().iterator();
    if (!entryItr.hasNext()) {
      return ImmutableMap.of();
    }
    Entry<K, ? extends V> entry1 = entryItr.next();
    K key1 = entry1.getKey();
    V value1 = entry1.getValue();
    checkEntryNotNull(key1, value1);
    // Do something that works for j2cl, where we can't call getDeclaredClass():
    EnumMap<K, V> enumMap = new EnumMap<>(singletonMap(key1, value1));
    while (entryItr.hasNext()) {
      Entry<K, ? extends V> entry = entryItr.next();
      K key = entry.getKey();
      V value = entry.getValue();
      checkEntryNotNull(key, value);
      enumMap.put(key, value);
    }
    return ImmutableEnumMap.asImmutable(enumMap);
  }

  /**
   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableMap} whose keys