About Question enthuware.ocpjp.v8.2.1870 :

[Kurospidey]

Code: Select all

List<Integer> names = Arrays.asList(1, 2, 3); //1
names.forEach(x->x=x+1); //2
names.forEach(System.out::println); //3

Can't get my head around //2. Isn't the assignment operator supposed to return the value assigned? In this case, forEach is expecting a Consumer but is receiving a UnaryOperator.

Shouldn't it be it will not compile due to code at //2?

[admin]

Try converting the lambda expression into a method. It will be:
void or return Type m(Type x){ //deliberately left out the return type because it will be determined by where you want to use it.
(return or no return) x = x+1;
}

Now, see if it fits the case for the functional interface required by forEach i.e. Consumer's accept method, which has the signature: void accept(T t).

Yes, void accept(T t) matches nicely with void m(Type x). There is no need for the return statement. Thus, even though x = x+1 has a return value, that value will not be returned back because the lambda expression will be translated to a method with a body that doesn't have any return value statement.

HTH,
Paul.

[Kurospidey]

Thanks! That one was tricky.

[jabenitez]

Hi,

I have the following questions:

- When the values of streams are changed?
- When the values of Collections.forEach are changed?

I've seen questions where they aren't changed.


Thanks in advance.

[admin]

I am not sure I understand your questions. Can you post code to explain what you mean?

[d0wnvk@gmail.com]

I am not sure I understand your questions. Can you post code to explain what you mean?

I think the question was:
what the exact conditions
- caused the underlaying collection's elements get changed ?
- caused the stream collection's element get chanded ?

we know, that we have likely two collections in a stream situation: the first which is original (underlaying) collection, and the second which is likely 'virtual' collection, built upon underlaying colletion.

Stream can transform data, but cannot mutate data - cannot understand this statement...