About Question enthuware.ocpjp.ii.v11.2.3331 :

[entitybean]

Why is this question in the category "09 - Parallel Streams"?

Question and answer options don't talk about parallel streams at all!

[admin]

Yes, it should be in "Builtin Functional interface"
thank you for your feedback!

[kabanvau]

Using Stream<Double> and BinaryOperator<Double>:
BinaryOperator<Double> bo =  (a, b)->a+b;
double total = bkStrm.map(b->b.getPrice()).reduce(dbo).get(); //reduce returns Optional<Double>, so, need to call get()
OR
double total = bkStrm.map(b->b.getPrice()).reduce(0.0, dbo).get(); //reduce returns Double

It should be:
double total = bkStrm.map(b->b.getPrice()).reduce(bo).get(); //reduce returns Optional<Double>, so, need to call get()
OR
double total = bkStrm.map(b->b.getPrice()).reduce(0.0, bo).get(); //without get()

[admin]

RIght. Fixed.
thank you for your feedback!

[carlosx]

on second option (and explanation):
double total = bkStrm.map(b->b.getPrice()).reduce((a, b)->{ return a+b;}).ifPresent(p->p.doubleValue());
The single parameter reduce method returns an OptionalDouble (if it is a DoubleStream) or Optional<Double> if it is Stream<Double>.
OptionalDouble has getAsDouble() that returns a Double and Optional<Double> has get() that returns a Double.

Shouldn't is say that the problem here is that ifPresent returns void?? is ok the explanation about the OptionalDouble but the real issue is you cant assign void to a variable. Looks to me that the explanation doesn't have anything about the issue or the real problem of this answer option.

[admin]

Yes, the explanation should explain that. Updated.
thank you for your feedback!

[dfigueira]

regarding the comment in the Explanation:

DoubleBinaryOperator dbo =  (a, b)->a+b;
double total = bkStrm.mapToDouble(b->b.getPrice()).reduce(dbo).getAsDouble(); //reduce returns OptionalDouble, so, need to call getAsDouble()
OR
double total = bkStrm.mapToDouble(b->b.getPrice()).reduce(0.0, dbo);//reduce returns Double

the mapToDouble returns a DoubleStream and the reduce method from that type of Stream returns a double instead of Double.

[admin]

You are right, it should say Double.

[dfigueira]

did you mean double?

[admin]

No, the code given there is bkStrm.map(b->b.getPrice()).reduce(0.0, bo)
Here, reduce returns Double.

[dfigueira]

I mean this one:
bkStrm.mapToDouble(b->b.getPrice()).reduce(0.0, dbo);

does it return a Double?

[admin]

Oh right. I see what you mean. Yes, it should be double. Fixed.
thank you for your feedback!

[aldabil]

Not fixed yet

[admin]

Could you please tell me where are you seeing it not fixed? I checked that is it fixed in 819 and 829 question banks.