Working with Streams and Lambda Expressions →hardMultiple ChoiceObjective-mapped

1Z0-829 Working with Streams and Lambda Expressions Practice Question

Given:

List<String> words = Arrays.asList("apple", "banana", "cherry"); Map<Integer, List<String>> map = words.stream().collect(Collectors.groupingBy(String::length)); System.out.println(map);

What is the output?

⚠ Common exam trap

Candidates often confuse `groupingBy` with `toMap` or assuming the map keys are the string values themselves, leading candidates to reverse the key-value roles or misrepresent the grouped lists.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

{5=[apple], 6=[banana, cherry]}

The `groupingBy` collector groups stream elements by a classifier function, here `String::length`. Each distinct length becomes a key in the map, and the values are lists of strings with that length. "apple" (length 5) maps to key 5, "banana" and "cherry" (both length 6) map to key 6, producing `{5=[apple], 6=[banana, cherry]}`.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
[apple, banana, cherry]
Why it's wrong here
That would be a list, not a map.
✗
{5=[5], 6=[6, 6]}
Why it's wrong here
Values are words, not lengths.
✓
{5=[apple], 6=[banana, cherry]}
Why this is correct
Correct grouping.
✗
{apple=[5], banana=[6], cherry=[6]}
Why it's wrong here
Map keys are lengths, not words.

Go deeper

1Z0-829 Working with Streams and Lambda Expressions Practice Question

Why each option matters

Option-by-option breakdown

Related to this question