Stream API Improvements

Most of the new Stream API features in Java 9 have already been demonstrated in the section that describes Stream filtering. To remind you, here are the examples we have demonstrated based on the Stream API improvements in JDK 9:

long c1 = senators.stream()
        .flatMap(s -> Stream.ofNullable(s.getParty() 
                              == "Party1" ? s : null))
        .count();
System.out.println("OfNullable: Members of Party1: " + c1);

long c2 = senators.stream()
        .map(s -> s.getParty() == "Party2" ? Optional.of(s) 
                                        : Optional.empty())
        .flatMap(Optional::stream)
        .count();
System.out.println("Optional.stream(): Members of Party2: "
                                                      + c2);

senators.stream().limit(5)
        .takeWhile(s -> Senate.timesVotedYes(s) < 5)
        .forEach(s -> System.out.println("takeWhile(<5): " 
                     + s + ": " + Senate.timesVotedYes...