Structural Patterns interview questions

Adapter, decorator, facade, proxy, and composite as answers to concrete design pressures.

3 questions in Low-Level Design & OOD.

Low-Level Design & Object-Oriented DesignA 23-minute read on how the topic fits together, before the questions.Low-level design fundamentals60 short answers on one page, for revising rather than studying.

medium2

mediumDesignCoding

A bundle can contain products or other bundles, and the pricing code should not care which it is holding. How would you model that?

A composite gives leaves and containers one interface so callers recurse without branching. The two decisions that matter are whether child management appears on that shared interface, and which operations genuinely aggregate - because price, availability and delivery date do not combine the same way. It also connects tree structures to the point an interviewer is testing.

6 minmid, senior, staff

mediumConceptDesign

Adapter, decorator and facade - what concrete problem does each one solve, and where would reaching for it be over-engineering?

Adapter converts a type you do not own into the interface your code already speaks. Decorator adds behaviour while keeping the same interface, so wrappers stack. Facade gives callers one narrow entry point into a subsystem. Each becomes over-engineering the moment nothing on the other side varies.

7 minmid, senior

hard1

hardDesignConcept

Your lazy-loading proxy works until someone calls equals or getClass on it. What breaks, and how do you design a proxy that survives it?

A lazy-loading proxy is a different object of a different class from its subject, so getClass comparisons, direct field reads and identity checks all see the proxy. A proxy pattern that survives defines equality by an identity key both sides answer without loading, compared through instanceof and accessors.

5 minmid, senior, staff