Course

Java and Python interview questions, explained

The language rules interviews probe, side by side and one language at a time: what the code really does, why, and what changed in each release.

Start free See the curriculum
  • 3 tracks
  • 36 skills
  • 144 lessons
  • 530 practice questions
  • 28 coding problems

What you'll learn

Side by Side covers the interview toolkit in both languages at once. Then each language gets its own track. Java: numbers and strings, collections, equality and immutability, class initialization, threads and the memory model, java.util.concurrent, and the features of Java 8, 17 and 21, virtual threads included. Python: the same essentials, the GIL, threads and processes, free-threaded Python, asyncio, and what Python 3.8 through 3.14 added.

Every output a lesson shows was produced by running the code, in the same Java 21 and Python sandboxes that grade your answers. Each wrong answer is tagged with the misconception it reveals, and some skills add coding problems that only make sense in that language.

The curriculum

Every skill has a lesson, a staff-level deep dive, a quick revise page and practice questions. Click a skill to read its lesson free.

Side by Side

1 skill

The interview toolkit in both languages at once - which structure, which call, and what it costs in each.

Java

19 skills

Java on its own: the essentials interviews test, multithreading and java.util.concurrent, and what Java 8, 17 and 21 - the long-term-support releases most codebases run - added.

Python

16 skills

Python on its own: the essentials interviews test, threads, processes and asyncio, and what each release from 3.8 to 3.14 added.

Problems locked to one language

Java-only coding problems

  • An Immutable BasketFree
  • Book a Meeting RoomFree
  • Clean Up a Contact ImportFree
  • Notification PreviewFree
  • Recently Viewed ItemsFree
  • Shipping Rates and LabelsFree
  • A Bounded Order QueuePro
  • A Bulkhead for a Fragile ServicePro
  • A Lazy, Retryable ConfigPro
  • A Revenue ReportPro
  • A Text Cleanup PipelinePro
  • A Worker That Stops on TimePro
  • Consistent Request StatsPro
  • Count Unique Sign-UpsPro
  • Count Words Across ThreadsPro
  • Fetch Partner QuotesPro
  • Money and Payment FeesPro
  • Payment Result MessagesPro
  • Price a Basket in ParallelPro
  • Rotate the CarouselPro
  • Subscription Renewal TimesPro
  • Top Words in Customer ReviewsPro

Python-only coding problems

  • Divide Like the LedgerPro
  • Fetch Every Quote at OncePro
  • Mirror a 32-bit RegisterPro
  • Price Tags in a SetPro
  • The Last SeatsPro
  • Top Pages by VisitsPro

Questions

Is this useful if I only use one language?

Yes. Set Java or Python as your language and code examples open in it. The Java and Python tracks each go deep on one language, so you can skip the other.

Does it cover Java 21 virtual threads and Python's free-threaded build?

Yes. The Java 21 module covers virtual threads and structured concurrency, and the Python track covers free-threaded Python and subinterpreters alongside the GIL, threading and multiprocessing.

What's free in the Java and Python course?

All 144 lessons and 530 practice questions are free. Pro unlocks the language-specific coding problems.

More courses

DSA interview prepPatterns from arrays to dynamic programming, graded by hidden tests.Object-oriented designSOLID, design patterns and nine projects graded by hidden suites.SQL practicePostgreSQL 18, hidden datasets and query-tuning labs.System designThe building blocks, then four designs checked by rules.

Start the Java & Python course free

No card needed. Upgrade to Pro when you want the full problem bank.

Start free See pricing

Free plan, no card · 7-day Pro trial · Cancel anytime