Four Pipelines: Write Down What Comes Out of Each

Four pipelines over the same five words. Write down the output of each, or that nothing happens, before opening the reveal.

java

List<String> words = List.of("pear", "fig", "apple", "fig", "plum");

// 1
words.stream().filter(w -> w.length() > 3).map(String::toUpperCase);
// 2
words.stream().distinct().count();
// 3
words.stream().map(w -> w.split("")).toList();
// 4
words.stream().flatMap(w -> Arrays.stream(w.split(""))).distinct().sorted().limit(3).toList();

What each of the four produces

Each pipeline, its result, and why
	Result	Why
1	Nothing happens at all	No terminal operation, so the description is built and discarded
2	`4`	`distinct` removes the second `fig` before `count` runs
3	A list of five arrays	`map` returns one value per element, and that value is an array
4	`[a, e, f]`	`flatMap` flattens the letters, then distinct, then sorted, then the first three

The third is the one that produces a type nobody wanted. A List<String[]> in the middle of a pipeline is the signature of a map that should have been a flatMap.

The fourth is worth tracing for the laziness: limit(3) means sorted still has to see everything — sorting cannot produce its first element until it has them all — while a limit before a sorted would not.