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Java Challenge #2

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Ended on 20 Sep
Free entry40 MCQs~1 hoursingle attemptlive leaderboardcore Java 17
Winner gets 3,000 credits + certificate
60+ registered
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Final standings(winners)
UserRankScore %
Bangaru K.Bangaru K.
199.9
Srilatha P.Srilatha P.
297.7
Bolla H.Bolla H.
397.7
AmrutyaAmrutya
495.8
A

Competition Details

40 at Abekus
40Total Questions
13 days at Abekus
13 daysChallenge Duration
6 - 20 Sep at Abekus
6 - 20 SepStarts: 5:30 AM - Ends: 5:29 AM
60 at Abekus
60Users Registered

Overview

You can write Java. But can you say exactly what it does?

Forty questions run across core Java — the object model, collections, generics and erasure, exception flow, strings, streams and concurrency. Most put real code in front of you and ask what it prints, what it throws, or why it compiles when you expect it not to. Every answer comes with an instant explanation, so you leave knowing which corners of the language you have solid.

  • Format — 40 MCQs, timed one by one, single attempt, live leaderboard
  • Scope — core Java and the standard library on Java 17; no Spring, no build tools
  • Level — assumes you have written real Java; builds from approachable to genuinely tricky
  • Marking — 1, 2 or 3 marks by difficulty, with a one-third penalty for a wrong answer
  • Top reward — 3,000 credits, an achievement certificate and a month of premium profile

Sequel to Java Challenge #1. Trace carefully, commit early, top the board.

Skills

Java

What you'll be tested on

  • Trace inheritance, overriding and initialisation order to predict what a program prints
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Amrutha V.
5
95.3
Apply the equals and hashCode contract, and predict lookup failures when it is broken
  • Choose between collection implementations by their real ordering and mutability guarantees
  • Recognise iterator invalidation and when ConcurrentModificationException is thrown
  • Reason about type erasure and bounded wildcards, including where an unchecked cast fails
  • Predict exception flow through finally, try-with-resources and suppressed exceptions
  • Spot integer overflow, integer division and autoboxing-cache identity traps
  • Explain stream laziness, short-circuiting, and why a pipeline without a terminal operation does nothing

    • Prize Pool

    Winner
    TOP PRIZEWinner
    3,000
    First Runner-Up
    First Runner-Up
    2,000
    Second Runner-Up
    Second Runner-Up
    1,000
    4–10
    500
    11–100
    100
    101–1000
    50

    About this competition

    Java Challenge #2 is the sequel to a round that drew 540 entrants, and it moves the emphasis from recall to reasoning. Forty multiple-choice questions cover the parts of Java where confident developers are most often wrong — not because the syntax is hard, but because the behaviour is not what the code appears to say.

    Object model and equality — inheritance and overriding versus hiding, constructor and initialiser order, the equals and hashCode contract, and what happens to a mutable key already inside a HashMap.

    Collections — the ordering guarantees each implementation actually makes, iterator invalidation and ConcurrentModificationException, the difference between the List returned by Arrays.asList and List.of, and remove(int) versus remove(Object).

    Generics — type erasure and what survives to runtime, bounded wildcards and why a List of a subtype is not a subtype of a List, and where an unchecked cast fails.

    Exceptions — the order of finally against return, try-with-resources and suppressed exceptions, and which exceptions the compiler forces you to acknowledge.

    Strings and numbers — interning and identity, immutability, integer overflow, integer division, floating-point comparison, and the autoboxing cache that makes small Integers compare equal by reference and larger ones not.

    Streams and concurrency — laziness and short-circuiting, why a stream with no terminal operation does nothing, reduce and collect semantics, and the basic visibility and atomicity problems that make an unsynchronised counter lose increments.

    Every question is timed on its own, sized to the reading and tracing it needs, so there is no global clock to manage. Harder questions carry more marks, and a wrong answer costs a third of them — so an honest skip beats a guess. Rewards are credits only, from 3,000 at rank 1 down to 40 at rank 10,000, with certificates for the top 100.

    Rules & guidelines

    Rules

    • SnapQuiz format: answer the MCQs shown, one attempt only.
    • Pick the correct option and respond as quickly as you can—your pace decides ties.
    • Marking: an easy question is worth 1 mark, a medium one 2 and a hard one 3. Every wrong answer carries a penalty of one third of that question's marks, so on a question you cannot narrow down, leaving it unanswered costs you less than a guess.
    • Your score is a percentage of the marks available on your own paper, so everyone is ranked on the same scale.
    • Every question is individually timed; when its timer ends the round advances, so unused time cannot be banked.
    • Questions are randomised, so no two attempts look alike.
    • Ranking updates live on the leaderboard.
    • Rewards are assigned by your final rank.
    • All participants are eligible for rewards within the published rank bands.

    Tips to get your best score

    • Find a quiet spot and a block of time where you won't be interrupted — on a timed round, a distraction-free setup does more for your score than almost anything else.
    • Read the whole snippet before you answer. Most questions turn on one line, and the trap is usually a detail you skipped past.
    • Trace by hand rather than by intuition. Writing two lines of state on paper beats trying to hold a loop in your head.
    • Decide, then commit. A calm first decision scores better than second-guessing and switching between options.
    • Use a laptop or desktop with a stable connection — code snippets are far easier to read at full width, and you'll move at full pace.
    • Warm up first: a quick review of collections, generics, exception flow and streams beforehand means you spend the round reasoning rather than remembering.

    Additional notes

    • Core Java only. No Spring, no build tools, no frameworks — just the language and the standard library.
    • Code is shown as it would compile and run on Java 17.
    • Each question carries its own time limit, sized to the reading and tracing it actually needs. When it runs out the round moves on.
    • Rewards for this challenge are credits only — no gems are issued.
    • Certificates go to the top 100 (achievement for the top 10, participation for ranks 11–100), and the top 10 also receive one month of a premium profile.

    Frequently asked questions

    What is Java Challenge #2 and what does it test?
    It is a timed, 40-question multiple-choice challenge over core Java: the object model and inheritance, the Collections framework, generics and type erasure, exception flow, strings and immutability, streams and lambdas, and concurrency basics. Most questions put real code in front of you and ask what it prints, what it throws, or why it compiles when you would expect it not to.
    Is this the same as Java Challenge #1?
    It is the sequel, not a rerun. The question set is entirely new and leans further into behaviour you have to reason about — equals/hashCode contracts, autoboxing caches, integer overflow, erasure, stream laziness and short-circuiting — rather than syntax recall. If you sat #1, nothing here will be familiar.
    What Java version is the code written against?
    Java 17. Every snippet is shown as it would actually compile and run, and each keyed answer was verified by executing the code rather than by inspection. Where behaviour depends on a version-specific detail, the question says so.
    Do I need to know Spring or build tools?
    No. This is core Java and the standard library only — no Spring, no Maven or Gradle, no application servers, no third-party libraries. If you know the language you have everything you need.
    How does scoring and ranking work?
    Questions are weighted by difficulty: an easy question is worth 1 mark, a medium one 2 and a hard one 3. A wrong answer carries a penalty of one third of that question's marks, so on a question you cannot narrow down, leaving it blank costs less than a guess. Your score is expressed as a percentage of the marks available on your own paper, so everyone is ranked on the same scale even though the specific questions differ. Ranking updates live while the challenge is open, and if two people finish level the faster average answering time takes the higher rank.
    How long does the challenge take?
    Plan for about an hour. There is no single global clock — each of the 40 questions carries its own time limit, sized to the reading and tracing it needs, from around a minute for a short trace up to three minutes for the longest. When a question's timer ends the round moves on, so you cannot bank unused time or pause partway.
    Should I practise before entering?
    Yes — a warm-up measurably helps. Practise Java on Abekus at your own pace beforehand, particularly collections, generics, exception flow and streams. The questions reward being able to trace code accurately under time pressure, which is a different skill from writing it.
    Is this suitable if I am still learning Java?
    Yes, with a caveat. The early questions are approachable for anyone who has written a few hundred lines of Java, and difficulty builds through the round. It does assume you have used collections and written a class or two — it is not a first-week introduction.
    What do I get if I rank well?
    Rewards for this challenge are credits only — no gems are issued. Rank 1 earns 3,000 credits, rank 2 earns 2,000, rank 3 earns 1,000, ranks 4–10 earn 500 each, ranks 11–100 earn 100 each, ranks 101–1,000 earn 50 each, and ranks 1,001–10,000 earn 40 each. Credits unlock premium features and content on Abekus.
    Will I get a certificate?
    Yes, for ranks in the top 100. The top 10 earn an achievement certificate plus one month of a premium profile, and ranks 11–100 earn a participation certificate. Both are issued once the round closes and final ranks are confirmed.
    Will this help me prepare for interviews?
    Yes. Reading unfamiliar code and predicting its behaviour is the core of most Java interview screens, and the traps here are the ones interviewers reach for: equals without hashCode, mutating a collection while iterating it, autoboxing identity, erasure, and stream operations that never run because nothing consumed them.
    Do I need to install anything to take part?
    No. The challenge runs entirely in your web browser on Abekus — nothing to download, no compiler needed. You just need a stable connection and an uninterrupted block of time. A laptop or desktop is strongly recommended, since code snippets are much easier to read at full width.
    1001–10000
    40

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