public static void main(String... args) {

    /*
    -------------------------------------------------------------------------
    From obj to ...
    -------------------------------------------------------------------------
    */
    Stream<String> streamOfStrings = Stream.of("un", "deux", "trois");
    Function<String, StringBuilder> function = StringBuilder::new;
    streamOfStrings.map(function) /*.forEach(System.out::println)*/;
    streamOfStrings = Stream.of("un", "deux", "trois");
    ToIntFunction<String> toIntFunction = String::length;
    IntStream streamOfInts = streamOfStrings.mapToInt(toIntFunction);
    streamOfStrings = Stream.of("un", "deux", "trois");
    ToDoubleFunction<String> toDoubleFunction = String::length;
    DoubleStream streamOfDoubles = streamOfStrings.mapToDouble(toDoubleFunction);
    streamOfStrings = Stream.of("un", "deux", "trois");
    ToLongFunction<String> toLongFunction = String::length;
    LongStream streamOfLongs = streamOfStrings.mapToLong(toLongFunction);

    /*
    -------------------------------------------------------------------------
    From int to ...
    -------------------------------------------------------------------------
    */
    IntUnaryOperator plusplus = i -> i++;
    IntStream.of(1, 2, 3).map(plusplus)
    /*.forEach(x->System.out.println(x))*/ ;
    IntFunction<String> intFunction = i -> "" + i;
    IntStream.of(1, 2, 3).mapToObj(intFunction)
    /*.forEach(System.out::println)*/ ;
    IntToDoubleFunction itdf = i -> i;
    IntStream.of(1, 2, 3).mapToDouble(itdf)
    /*.forEach(System.out::println)*/ ;
    IntToLongFunction itlf = i -> i;
    IntStream.of(1, 2, 3).mapToLong(itlf)
    /*.forEach(System.out::println)*/ ;

    /*
    -------------------------------------------------------------------------
    From long to ...
    -------------------------------------------------------------------------
    */
    LongUnaryOperator times = l -> l * l;
    LongStream.of(1L, 2L, 3L).map(times)
    /*.forEach(System.out::println)*/ ;
    LongFunction<String> lf = l -> "toto";
    LongStream.of(1L, 2L, 3L).mapToObj(lf);

    /*
    -------------------------------------------------------------------------
    From double to ...
    -------------------------------------------------------------------------
    */
    DoubleToIntFunction dtif = d -> (int) d;
    DoubleStream.of(1.3, 1.5, 1.6).mapToInt(dtif).forEach(System.out::println);
  }
 @Override
 public LongStream perform(Stream<I> stream) {
   return stream.mapToLong(function);
 }