Question/Errata for OCP:Oracle Certified Professional Java SE 8 Programmer II Study Guide - page 557

[Guillaume Bailly]

Hi,

For the answer to question 14 on page 557, I was wondering if the second "autoboxing" shouldn't be understood as "unboxing" since we are converting to a primitive like explained?

Thanks for your answer.

Kind regards,
Guillaume

[Jeanne Boyarsky]

Guillaume,
You are correct and I logged it. This is a case of "sloppy" English.

Autoboxing does mean primitive to object and unboxing means object to primitive. Sometimes people (incorrectly) use autoboxing to refer to both ways. I mention this because you could easily encounter this "sloppy English" problem in other books or even when talking to people in the workplace. Which means it is good to be suspicious when you hear "autoboxing" and consider it might be meant either way.

[Guillaume Bailly]

Thanks for the explanation. I will pay attention in the future, now even more :-)

[Juerg Bauman]

4: Stream<Integer> s = Stream.of(1);
5: IntStream is = s.mapToInt(x -> x);
6: DoubleStream ds = s.mapToDouble(x -> x);
7: Stream<Integer> s2 = ds.mapToInt(x -> x);
8: s2.forEach(System.out::print);

The explanation says: Converting from a double to an int would require a cast inside the lambda, but
7: Stream<Integer> s2 = ds.mapToInt(x -> (int)x); still doesn't work. mapToInt has to be replaced by mapToObject.
Furthermore line 6 throws an IllegalStateException: stream has already been operated upon

Stream<Integer> s = Stream.of(1);
IntStream is = s.mapToInt(x -> x);
s = Stream.of(1);
DoubleStream ds = s.mapToDouble(x -> x);
Stream<Integer> s2 = ds.mapToObj(x -> (int)x);
s2.forEach(System.out::print);

[Jeanne Boyarsky]

Juerg Bauman wrote:The explanation says: Converting from a double to an int would require a cast inside the lambda, but
7: Stream<Integer> s2 = ds.mapToInt(x -> (int)x); still doesn't work. mapToInt has to be replaced by mapToObject.

Actually mapToObj. And yes, I've added that to the errata. A cast isn't needed in any event.

Juerg Bauman wrote:Furthermore line 6 throws an IllegalStateException: stream has already been operated upon

While that's true, the question and explanation are about compiling. The runtime exception is a "decoy" answer to try to trick you.