Interviews and Capstone

A Core Java interview bank, OOP and design questions, tricky output puzzles verified on a real JDK, and a library management system built end to end.

This phase turns everything in the course into two things you can use: interview answers and a working program. An interview checks whether you can explain an idea clearly, show the mechanism underneath it, and name the trap that catches people. Every answer here does those three things, and each one points to the topic that teaches the subject in full, so a weak answer becomes a reading list.

Topic 16.1 is a large bank of Core Java questions, grouped the way interviewers ask them: the JVM, Strings, equals and hashCode, collections internals, exceptions, generics, OOP, modern Java from 8 to 21, concurrency and garbage collection. Topic 16.2 covers object-oriented design questions: SOLID, composition, immutability and the classic "design a class for…" prompts, linking to the System Design course where the patterns are taught in depth. Topic 16.3 is a set of tricky output questions: small programs where you predict the output before you run them. Every output on that page was produced by a real JDK, not typed from memory.

Topic 16.4 is the capstone: a small library management system built step by step with records, enums, sealed interfaces, collections, streams, exceptions, Optional and java.time. It ends with one runnable file you can extend with the practice tasks. If you can build it without looking, and answer most of the questions in 16.1 and 16.2 out loud, you are ready for a Java developer interview.