functional programming - Have to work with object which has Set of enties using Java 8? -

i have implement method following signature:

public set<event> getfordaterange(calendar from, calendar to) 

my event class looks like:

public class event {      private integer id;     private string name;     private integer price;     private rating rating;      private set<calendar> eventdatetime; 

i can not find how datetimes event. here have far:

public set<event> getfordaterange(calendar from, calendar to) {     set<event> result = collections.emptyset();     set<event> allevents = getall();     (event event : allevents) {         set<calendar> eventdatetime = event.geteventdatetime();         result.addall(eventdatetime.stream()                 .filter(date -> date.after(from) && date.before(to))                 .map(date -> event)                 .collect(collectors.toset()));     }     return result; } 

i using mixture of iterative style functional. how write method using functional style only?

your current code bit weird: .map(date -> event) mapping dates same event.

what want retain events such 1 of event time between from , to. can obtain anymatch. operation returns whether of stream element matches given predicate. in case, if dates between from , to, keep event , collect set.

public set<event> getfordaterange(calendar from, calendar to) {     set<event> allevents = getall();      return allevents.stream()             .filter(event -> event.geteventdatetime()                     .stream()                     .anymatch(date -> date.after(from) && date.before(to))             )             .collect(collectors.toset()); }