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46+ curated questions with the same answer shape every time: quick recap, deep dive, pitfalls, and follow-ups. Coverage includes builder pattern, comparisons, decorator pattern, factory and abstract factory, and more.
Suggested path
Topics follow a teaching order. Each answer ends with a clear Next question control so you can move forward without hunting the list.
Design patterns are the vocabulary senior engineers use to describe solutions, and freshers who know them stand out immediately. This module focuses on the patterns that appear in Java and Spring Boot codebases every day — Singleton (and why Spring beans are singletons), Factory (how Spring creates beans), Builder (Lombok @Builder, StringBuilder), Strategy (payment method selection, sorting algorithms), and Observer (Spring events, React state callbacks). SOLID principles are taught as the diagnosis tool: when an interviewer asks you to improve a piece of code, naming which SOLID principle it violates is the clearest way to structure your answer.
Full catalog
Topics are ordered for learning. Within each topic, rows are numbered 1–46 globally so you always know where you are. Collapse topics if you want a lighter view — use Expand all when you need the full list again.
Numbers 1–46 follow the order we recommend — click any row to open the full answer, or use the sticky Next link at the bottom of each page to go Q1 → Q46.