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in28minutes/JavaInterviewQuestionsAndAnswers
Java Interview Questions and Answers
A companion repo to an in28minutes Udemy course: 220+ Java interview questions organized by topic, with markdown answer docs and matching runnable example code for most sections. Aimed at developers cramming for Java interviews, particularly around core language, OOP, collections, and concurrency.
The topic ordering is a genuinely useful study path (basics to OOP to exceptions to collections to generics to threads to streams), so it doubles as a curriculum, not just a Q&A list. Several tricky topics are backed by actual code instead of prose, e.g. FailFast.java/FailSafe.java for iterator behavior and ConcurrentCollectionsExamples.java for the concurrent collections questions, so you can run and step through the behavior yourself. The docs/ folder mirrors the paid course content for free, giving real written answers rather than just question stubs.
Dead since November 2023 and it shows: nothing on records, sealed classes, pattern matching, or virtual threads, and the 'New Features' section stops at Java 8. The README itself is structured as a funnel to the paid Udemy course (course banner, coupon link, PDF gated behind the course) rather than a self-contained reference. Quality is uneven — several questions are just 'guess the output' with no inline explanation, and the maintainer left a known-wrong answer for question 86 uncorrected rather than fixing it. There's no test suite or CI, so nothing verifies the example code still compiles or behaves as described.