*
   * <p>If the mapped keys contain duplicates (according to the specified comparator), an {@code
   * IllegalArgumentException} is thrown when the collection operation is performed. (This differs
   * from the {@code Collector} returned by {@link Collectors#toMap(Function, Function)}, which
   * throws an {@code IllegalStateException}.)
   *
   * @since 33.2.0 (available since 21.0 in guava-jre)
   */

 * common ways to create a {@code ListenableFuture} include instantiating a {@link SettableFuture},
 * submitting a task to a {@link ListeningExecutorService}, and deriving a {@code Future} from an
 * existing one, typically using methods like {@link Futures#transform(ListenableFuture,
 * com.google.common.base.Function, java.util.concurrent.Executor) Futures.transform} and {@link

   * iterated are the individual lists created, and these are not retained after iteration.
   *
   * @param sets the sets to choose elements from, in the order that the elements chosen from those
   *     sets should appear in the resulting lists
   * @param <B> any common base class shared by all axes (often just {@link Object})

 */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
public final class Multimaps {
  private Multimaps() {}

  /**
   * Returns a {@code Collector} accumulating entries into a {@code Multimap} generated from the
   * specified supplier. The keys and values of the entries are the result of applying the provided
   * mapping functions to the input elements, accumulated in the encounter order of the stream.
   *
   * <p>Example:
   *

    Iterator<Integer> result =
        Iterators.transform(
            input,
            new Function<String, Integer>() {
              @Override
              public Integer apply(String from) {
                return Integer.valueOf(from);
              }
            });

    List<Integer> actual = Lists.newArrayList(result);
    List<Integer> expected = asList(1, 2, 3);
    assertEquals(expected, actual);
  }

   * Removes every element that satisfies the provided predicate from the iterator. The iterator
   * will be left exhausted: its {@code hasNext()} method will return {@code false}.
   *
   * @param removeFrom the iterator to (potentially) remove elements from
   * @param predicate a predicate that determines whether an element should be removed
   * @return {@code true} if any elements were removed from the iterator
   * @since 2.0
   */