Is there a way to return an Object from stream after Filter? Getting ClassCastException

Question

I want to return an object from a list via a stream.

return (planlinevaluesEntityList != null ? (PlanlinevaluesEntity) planlinevaluesEntityList.stream()
            .filter(p -> p.getMandantKagId()
                    .equals(Long.valueOf(mkId))) : null);

But I get a ClassCastException:

java.lang.ClassCastException: class java.util.stream.ReferencePipeline$2 cannot be cast to class de.pares.int_plan.entity.PlanlinevaluesEntity...

I also tried to use "findFirst()"..

Can anyone tell me what I am doing wrong?

Answer 1

Any Stream operation required a Terminal operation to return anything else than a Stream. In your case, you have multiple choices: findAny() or findFirst(). Both return an Optional<T> that you can unwrap using orElse(null).

If you need an explicit cast, just like in your question, you can use filter and map like hereunder

if (planlinevaluesEntityList == null) {
    return null;
}
return planlinevaluesEntityList.stream()
                               .filter(p -> p.getMandantKagId()
                                             .equals(Long.valueOf(mkId))
                               )
                               .filter(PlanlinevaluesEntity.class::isInstance)
                               .map(PlanlinevaluesEntity.class::cast)
                               .findFirst()
                               .orElse(null);