Do I need to check for null input when implementing java.util.function.Function<T,R>

Question

When using java8 stream API

.stream().map(mapper)

is it neccessary in the mapper's apply(T t) method implemented as java.util.function.Function<T,R> check for null input t ? Or is it guaranteed that the apply(T t) method is never called with null argument even when my stream() -ed Collection contains null s?

In another words,

    .stream().map(mapper)

allows null values to be passed into apply(T t) and does not throws NullPointerException ?

Answer 1

It depends on whether you expect a null as an input. In general you will want to avoid using null is a stream (or throwing check exceptions). You can do

list.stream()
    .filter(x -> x != null)
    .... do more

Note if you do

Stream.of("hi", null).forEach(System.out::println);

will print

hi
null

See http://ideone.com/eoQ3so