Given the definition of the Country class: public class Country { public enum Continent {ASIA, EUROPE} String name; Continent region; public Country (String na, Continent reg) { name = na; region =…

Question

Options

• A{EUROPE = [Italy, Germany], ASIA = [Japan]}
• B{ASIA = [Japan], EUROPE = [Italy, Germany]}
• C{EUROPE = [Germany, Italy], ASIA = [Japan]}
• D{EUROPE = [Germany], EUROPE = [Italy], ASIA = [Japan]}

• A
  83% (38)
• B
  2% (1)
• C
  11% (5)
• D
  4% (2)

Explanation

Option A is correct because Collectors.groupingBy uses a HashMap internally (no guaranteed key order), and Collectors.mapping preserves encounter order within each group - Italy appears before Germany in the original list, so the EUROPE list is [Italy, Germany], not [Germany, Italy]. Option C is wrong for exactly this reason: it reverses Italy and Germany within the EUROPE group, violating encounter order. Option D is wrong because a Map cannot have duplicate keys - groupingBy merges all entries sharing a key into a single List, not separate entries. Option B has the correct values but shows ASIA before EUROPE; while HashMap order is technically undefined, exam questions typically expect the output that the JVM produces for the given hash codes, which puts EUROPE first here. Memory tip: Think of groupingBy + mapping as "sort into buckets, then transform what's in each bucket" - the bucket contents always stay in the order they were encountered in the stream.

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