code: public static <T, K, U> Collector<T, ?, LinkedHashMap<K, U>> toLinkedMap(Function<? super T, ? extends K> keyMapper,
                                                                               Function<? super T, ? extends U> valueMapper) {
          BinaryOperator<U> mergeFunction = throwingMerger();
          return toLinkedMap(keyMapper, valueMapper, mergeFunction);
      }
docs: Collects a stream to a LinkedHashMap, each stream element is expected to produce map entry.
  @param keyMapper   function to deal with keys.
  @param valueMapper function to deal with values.
  @param <T>         type of element in input stream.
  @param <K>         type of key for created map.
  @param <U>         type of value for created map.
  @return map with a key/value for each item in the stream.
  @throws IllegalArgumentException if keyMapper produces the same key multiple times.