Java Streams Quiz

Which of the following does not create a Java Stream?

• List.of("a","b").stream()

• Arrays.stream(new int[]{1,2,3})

• Stream.of("x","y","z")

• new Stream()

What does it mean that Java Streams are “lazy”?

• They pause between elements.

• Intermediate operations don’t run until a terminal operation is invoked.

• They execute on a background thread.

• They cache all elements in memory.

Which of the following is a terminal Stream operation?

• filter(...)

• map(...)

• sorted()

• collect(...)

What is the result of this code? List names = List.of("Ana","Bob","Cip"); long c = names.stream() .filter(s -> s.length() > 3) .count(); System.out.println(c);

• 3

• 2

• 1

• 0

Given List.of(3,1,2,3,2), what does .stream().distinct().sorted().toList() produce?

• [1,2,3]

• [3,2,1]

• [3,1,2,3,2]

• [2,3,1]

Which operation would you use to convert a Stream> into a Stream?

• map(...)

• flatMap(...)

• collect(...)

• filter(...)

What does this do? List nums = List.of(2,3,4); int result = nums.stream().reduce(1, (a,b)->a*b);

• Concatenates numbers as strings

• Calculates the product (24)

• Throws an exception

• Calculates sum (9)

What is the return type of Collectors.groupingBy(...) in Java Streams?

• Map

• List

• Set

• Collection

Collectors.mapping(Person::getName, Collectors.toList()) produces:

• Map

• List

• Set

• Collection

How do you safely extract a value from an Optional opt with a default of "N/A"?

• opt.get()

• opt.orElse("N/A")

• opt.orThrow()

• opt.getOr("N/A")