takeWhile() working differently with flatmap

Question

I am creating snippets with takeWhile to explore its possibilities. When used in conjunction with flatMap, the behaviour is not in line with the expectation. Please find the cod

Answer 1

The reason for that is the flatMap operation also being an intermediate operations with which (one of) the stateful short-circuiting intermediate operation takeWhile is used.

The behavior of flatMap as pointed by Holger in this answer is certainly a reference one shouldn't miss out to understand the unexpected output for such short-circuiting operations.

Your expected result can be achieved by splitting these two intermediate operations by introducing a terminal operation to deterministically use an ordered stream further and performing them for a sample as :

List sampleList = Arrays.stream(strArray).flatMap(Arrays::stream).collect(Collectors.toList());
sampleList.stream().takeWhile(ele -> !ele.equalsIgnoreCase("Sample4"))
            .forEach(System.out::println);

Also, there seems to be a related Bug#JDK-8075939 to trace this behavior already registered.

Edit: This can be tracked further at JDK-8193856 accepted as a bug.