Fetch first element which matches criteria

Question

How to get first element that matches a criteria in a stream  I ve tried this but doesn t work  this stops stream   filter Stop s- gt  s getStation   getName   equals name      That criteria is not working  the filter method is invoked in an other class than Stop   public class Train    private final String name  private final SortedSet lt Stop gt  stops   public Train String name        this name   name      this stops   new TreeSet lt Stop gt        public void addStop Stop stop        this stops add stop      public Stop getFirstStation         return this getStops   first       public Stop getLastStation         return this getStops   last       public SortedSet lt Stop gt  getStops         return stops     public SortedSet lt Stop gt  getStopsAfter String name             return this stops subSet   toElement       return null        import java util ArrayList  import java util List   public class Station   private final String name  private final List lt Stop gt  stops   public Station String name        this name   name      this stops   new ArrayList lt Stop gt         public String getName         return name

User · Accepted Answer

This might be what you are looking for  yourStream      filter    your criteria          findFirst        get     And better  if there s a possibility of matching no element  in which case get   will throw a NPE  So use  yourStream      filter    your criteria          findFirst        orElse null      You could also create a default object here       An example  public static void main String   args        class Stop           private final String stationName          private final int    passengerCount           Stop final String stationName  final int passengerCount                this stationName      stationName              this passengerCount   passengerCount                       List lt Stop gt  stops   new LinkedList lt  gt          stops add new Stop  quot Station1 quot   250        stops add new Stop  quot Station2 quot   275        stops add new Stop  quot Station3 quot   390        stops add new Stop  quot Station2 quot   210        stops add new Stop  quot Station1 quot   190         Stop firstStopAtStation1   stops stream                filter e - gt  e stationName equals  quot Station1 quot                 findFirst                orElse null        System out printf  quot At the first stop at Station1 there were  d passengers in the train  quot   firstStopAtStation1 passengerCount      Output is  At the first stop at Station1 there were 250 passengers in the train

User · Answer

I think this is the best way  this stops stream   filter s - gt  Objects equals s getStation   getName    this name   findFirst   orElse null

User · Answer

When you write a lambda expression  the argument list to the left of - gt  can be either a parenthesized argument list  possibly empty   or a single identifier without any parentheses   But in the second form  the identifier cannot be declared with a type name   Thus   this stops stream   filter Stop s- gt  s getStation   getName   equals name      is incorrect syntax  but  this stops stream   filter  Stop s - gt  s getStation   getName   equals name      is correct   Or   this stops stream   filter s - gt  s getStation   getName   equals name      is also correct if the compiler has enough information to figure out the types

[java] Fetch first element which matches criteria

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