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) {
          return Collectors.toMap(keyMapper, valueMapper, mergeFunction, LinkedHashMap::new);
      }
docs: Collects a stream to a LinkedHashMap.
  @param keyMapper   function to deal with keys.
  @param valueMapper function to deal with values.
  @param mergeFunction function to apply one values if keyMapper produces same key multiple times.
  @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.