How do elements of a stream go thought the stream itself? Is it like it takes 1 element and passes it thought all functions (map then sort then collect) and then takes second elements and repeats the cycle or is it like it takes all elements and maps them then sorts and finally collects?
new ArrayList<Integer>().stream()
.map(x -> x.byteValue())
.sorted()
.collect(Collectors.toList());
It depends entirely on the stream. It is usually evaluated lazily, which means it takes it one element at a time, but under certain conditions it needs to get all the elements before it continues to the next step. For example, consider the following code:
IntStream.generate(() -> (int) (Math.random() * 100))
.limit(20)
.filter(i -> i % 2 == 0)
.sorted()
.forEach(System.out::println);
This stream generates random numbers from 0 to 99, limited to 20 elements, after which it filters the numbers by checking wether or not they are even, if they are, they continue. Until now, it's done one element at a time. The change comes when you request a sorting of the stream. The sorted() method sorts the stream by the natural ordering of the elements, or by a provided comparator. For you to sort something you need access to all elements, because you don't know the last element's value until you get it. It could be the first element after you sort it. So this method waits for the entire stream, sorts it and returns the sorted stream. After that this code just prints the sorted stream one element at a time.