What if null is passed to apply method of Function Interface in java?

Question

userMap is a hashmap which contains userId as key.

userDtoTransformer.apply(userMap.get(userId));

What if there is no such userId present in the map? Then apply method will have null as argument. So, will it throw an exception?

Answer 1

apply method just calls your function with the passed argument. So your code would be equal to methodRepresentedByUserDtoTransformer(userMap.get(userId)) . So it behaves identical to this invocation, so if you don't have the user in your map then you would have the equivalent of call methodRepresentedByUserDtoTransformer(null) , and then it depends on how your method handles null arguments.