Fetch first element which matches criteria
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<Stop> stops = new LinkedList<>();
stops.add(new Stop("Station1", 250));
stops.add(new Stop("Station2", 275));
stops.add(new Stop("Station3", 390));
stops.add(new Stop("Station2", 210));
stops.add(new Stop("Station1", 190));
Stop firstStopAtStation1 = stops.stream()
.filter(e -> e.stationName.equals("Station1"))
.findFirst()
.orElse(null);
System.out.printf("At the first stop at Station1 there were %d passengers in the train.", firstStopAtStation1.passengerCount);
}
Output is:
At the first stop at Station1 there were 250 passengers in the train.
When you write a lambda expression, the argument list to the left of ->
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-> s.getStation().getName().equals(name));
is incorrect syntax; but
this.stops.stream().filter((Stop s)-> s.getStation().getName().equals(name));
is correct. Or:
this.stops.stream().filter(s -> s.getStation().getName().equals(name));
is also correct if the compiler has enough information to figure out the types.
I think this is the best way:
this.stops.stream().filter(s -> Objects.equals(s.getStation().getName(), this.name)).findFirst().orElse(null);