Top 12 Java Streams Interview Questions — map, filter, groupBy, reduce (With Code Examples)

Published: 14 April 2026
on channel: TechInterviewNotes

Master Java 8+ Stream API for your next interview! Covers stream basics, map/filter/reduce, Collectors (groupingBy, partitioningBy), flatMap, Optional, finding max/min, frequency count, removing duplicates, parallel streams, method references, and practical coding patterns.

Questions Covered:
00:00 Introduction
00:20 Q1. Stream API Basics & Pipeline
00:55 Q2. map, filter, reduce
01:25 Q3. Collectors.groupingBy
01:55 Q4. partitioningBy
02:25 Q5. flatMap
02:55 Q6. Optional
03:25 Q7. Finding Max/Min
03:55 Q8. Frequency Count & Duplicates
04:25 Q9. Removing Duplicates
04:55 Q10. Parallel Streams
05:25 Q11. Method References
05:55 Q12. Collection Conversions

#JavaStreams #Java8 #FunctionalProgramming #JavaInterview #StreamAPI #CodingInterview #JavaDeveloper #Lambda #Collections

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