Low-Level Design (Object-Oriented Design)
Low-Level Design (Object-Oriented Design) practice
38 exercises and 45 quizzes from the lessons of this track. Sample tests run in your browser; what you pass is kept in this browser only.
LLD rounds and a repeatable answer method
- Let a member give a copy back
- Quiz: What low-level design (LLD) is and what it tests
- Write the public API of a bike-sharing dock
- Quiz: A repeatable framework for LLD answers
- Turn a printer queue's rules into acceptance cases
- Quiz: Clarifying requirements and scope
- Give each requirement of an outpatient clinic one owner
- Quiz: Finding entities and assigning responsibilities
- Write the command dispatcher for a meeting-room service
- Quiz: The machine-coding round playbook
Designing objects for change
Class relationships and UML
- Keep both ends of a doctor-patient link in step
- Quiz: Class relationships in UML and code
- Write a library's class diagram as data
- Quiz: UML class diagrams that interviewers can read
- Record a booking service's calls as a sequence of messages
- Quiz: Sequence diagrams for key flows
- A food order's lifecycle as a transition table
- Quiz: UML state machine diagrams
- Turn a co-working app's requirements into use cases
- Quiz: Use case and activity diagrams
Design principles: SOLID and beyond
- Make the report's output format swappable
- Quiz: Coupling, cohesion and information hiding
- Split a report card that serves two groups of people
- Quiz: Single Responsibility Principle (SRP)
- Add two discount rules without editing Checkout
- Quiz: Open/Closed Principle (OCP)
- Write the contract tests for a queue
- Quiz: Liskov Substitution Principle (LSP)
- Split a school's staff interface into roles
- Quiz: Interface Segregation Principle (ISP)
- Inject the gateway, clock and ids of an order service
- Quiz: Dependency Inversion Principle (DIP)
- Give one rule one home, and keep two look-alikes apart
- Quiz: DRY, KISS and YAGNI without dogma
- Make three hotel call sites talk only to the booking
- Quiz: Law of Demeter, tell-don't-ask and CQS
- Place two car-rental responsibilities with GRASP
- Quiz: GRASP: assigning responsibilities
- Apply three changes to two designs, then weigh them
- Quiz: When design principles conflict
Modelling lifecycles, time, money and rules
- Turn a ticket's if statements into a transition table
- Quiz: Implementing lifecycles: State, tables or enums
- A courier shipment with three delivery attempts and duplicate scans
- Quiz: Designing lifecycles as state machines
- Seat holds that expire on an injected clock
- Quiz: Time in designs: clocks, time zones and timers
- An invoice total with dated tax rates and one rounding
- Quiz: Money arithmetic: paise, rounding and splits
- Wallet top-ups that are safe to retry
- Quiz: IDs, idempotency keys and deduplication
- A tax-rate table with effective dates and overlap checks
- Quiz: Rules as configuration: tables and effective dates
Testing your design
Code quality under time pressure
One design, six languages
- Quiz: LLD in Java 25: records, sealed types, patterns
- A canteen order rewritten with dataclasses, an enum and a protocol
- Quiz: LLD in Python 3.14: dataclasses and protocols
- Quiz: LLD in TypeScript with erasable syntax only
- Quiz: LLD in Go: interfaces, embedding, generics
- Quiz: LLD in modern C++: ownership and variants
- Quiz: LLD in Rust: traits, enums and ownership
Case studies: everyday machines
Machine-coding and interview practice
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