Handling Common Data Formats - Java in a Nutshell - page 283

return birthday ;
}

public LocalDate getBirthdayFor ( String name ) {
return birthdays . get ( name );
}

public int getAgeInYear ( String name , int year ) {
Period period = Period . between ( birthdays . get ( name ),
birthdays . get ( name ). withYear ( year ));

return period . getYears ();
}

public Set < String > getFriendsOfAgeIn ( int age , int year ) {
return birthdays . keySet (). stream ()
. filter ( p -> getAgeInYear ( p , year ) == age )
. collect ( Collectors . toSet ());
}

public int getDaysUntilBirthday ( String name ) {
Period period = Period . between ( LocalDate . now (),
birthdays . get ( name ));
return period . getDays ();
}

public Set < String > getBirthdaysIn ( Month month ) {
return birthdays . entrySet (). stream ()
. filter ( p -> p . getValue (). getMonth () == month )
. map ( p -> p . getKey ())
. collect ( Collectors . toSet ());
}

public Set < String > getBirthdaysInNextMonth () {
return getBirthdaysIn ( LocalDate . now (). getMonth ());
}

public int getTotalAgeInYears () {
return birthdays . keySet (). stream ()
. mapToInt ( p -> getAgeInYear ( p ,
LocalDate . now (). getYear ()))
. sum ();
}
}
This class shows how to use the low-level API to build up useful functionality. It
also uses innovations such as the Java Streams API, and demonstrates how to use
LocalDate as an immutable class and how dates should be treated as values.

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