HigherKindedTypes blog post code

Mappable.java

public interface Mappable<A> { 
  public <B> Mappable<B> map(Function<A, B> f); 
}

optionalMap.java

// assuming that getLastUserWhoLoggedIn might return null 
String timeZoneOfLastLoggedInUser = Optional.ofNullable(userService.getLastUserWhoLoggedIn()) // Optional<User> 
                                            .map(user -> user.getAddress()) // Optional<Address> 
                                            .map(address -> timeZoneService.getTimeZone(address)) // Optional<TimeZone> 
                                            .map(timeZone -> timeZone.toString()) // Optional<String>
                                            .orElse("UTC"); // safely "unwrapping" our Optional<String> to get just a String

painfulNesting.java

someListOfListsOfOptionals.stream() 
                          .flatMap(listOfOptionals -> listOfOptionals.stream()
                                                                     .map(optional -> optional.map(user -> user.getEmail() ).orElse("")) 
                          ) //...

parseNumbers.java

public List<Integer> parseNumbers(Function<String, Integer> numberParser, List<String> stringsToParse){ 
  // for every string in stringsToParse, run it through numberParser and add it to a list. 
}

streamMap.java

// assuming that we have a List<Integer> named someListOfIntegers
someListOfIntegers.stream() // gives us a Stream<Integer> 
                  .map(x -> x.toString()) // now we have a Stream<String>