Suppose to have a class Obj
class Obj{
int field;
}
and that you have a list of Obj
instances, i.e. List<Obj> lst
.
Now, how can I find in Java8 with streams the sum of the values of the int fields field
from the objects in list lst
under a filtering criterion (e.g. for an object o
, the criterion is o.field > 10
)?
This question is related to
java
filter
java-8
java-stream
You can try
int sum = list.stream().filter(o->o.field>10).mapToInt(o->o.field).sum();
Like explained here
In Java 8 for an Obj
entity with field
and getField() method you can use:
List<Obj> objs ...
Stream<Obj> notNullObjs =
objs.stream().filter(obj -> obj.getValue() != null);
Double sum = notNullObjs.mapToDouble(Obj::getField).sum();
Try:
int sum = lst.stream().filter(o -> o.field > 10).mapToInt(o -> o.field).sum();
You can do this method: "IntSummaryStatistics"
IntSummaryStatistics insum = li.stream().filter(v-> v%2==0).mapToInt(mapper->mapper).summaryStatistics();
You can also collect
with an appropriate summing collector like Collectors#summingInt(ToIntFunction)
Returns a
Collector
that produces the sum of a integer-valued function applied to the input elements. If no elements are present, the result is 0.
For example
Stream<Obj> filtered = list.stream().filter(o -> o.field > 10);
int sum = filtered.collect(Collectors.summingInt(o -> o.field));
Source: Stackoverflow.com