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Design a Coffee Vending Machine - Low-Level Design | OneNoughtOne

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Design a Coffee Vending Machine

Beginner

Design an object-oriented coffee vending machine that manages a catalogue of beverage recipes (espresso, latte, cappuccino, etc.), tracks ingredient inventory, and brews drinks on demand.

The system should support drink customisation (extra sugar, less milk), dynamically display only available beverages based on current stock levels, and handle the full workflow from selection through payment to dispensing.

Core Use Cases

Select a beverage

User chooses from a menu of available coffee drinks (espresso, latte, cappuccino, etc.)

Customise a drink

User adjusts ingredient quantities — extra sugar, less milk, add cream

Brew and dispense

Machine prepares the drink by consuming ingredients per the recipe and dispensing it

Check ingredient availability

Before brewing, verify all ingredients are sufficiently stocked

Display available menu

Dynamically show only beverages that can be made with current stock

Refill ingredients

Admin restocks ingredients when they run low

Payment handling

Accept payment and return change before dispensing

Constraints

Each beverage is defined by a recipe — a fixed set of ingredients and their quantities
The machine has finite ingredient reservoirs with known capacities
A beverage can only be made if all required ingredients are sufficiently stocked
Customisations adjust ingredient quantities but cannot add ingredients not in the base recipe
Only one beverage can be brewed at a time (sequential processing)

Assumptions

Payment is simplified — assume exact payment or simple change return
No temperature or brewing-time simulation
Ingredient units are standardised (ml for liquids, grams for solids)
Recipes are pre-configured at startup by an admin

In Scope

Recipe management and beverage catalogue
Ingredient inventory tracking
Availability-based menu generation
Drink customisation within recipe bounds
Brewing workflow (select → pay → dispense)

Out of Scope

Actual hardware control (grinder, heater, pump)
Temperature and brewing-time simulation
Credit/debit card payment integration
Remote monitoring and IoT connectivity
Cup size and lid management

Approach Guide(Click to expand each section)

Before diving into code, clarify the use cases and edge cases. Understanding the problem deeply leads to better class design.

List Core Use Cases

Identify the primary actions users will perform. For a parking lot: park vehicle, exit vehicle, check availability. Each becomes a method.

Identify Actors

Who interacts with the system? Customers, admins, automated systems? Each actor type may need different interfaces.

Clarify Constraints

What are the limits? Max vehicles, supported vehicle types, payment methods. Constraints drive your data structures.

Ask About Edge Cases

What happens on overflow? Concurrent access? Payment failures? Thinking about edge cases reveals hidden complexity.

Follow-up Questions(Questions an interviewer might ask)

💡 Draw UML class diagrams, sequence diagrams, or any design visualizations. Submit from the Code tab.

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00:00:00

Design a Coffee Vending Machine

Beginner

Design an object-oriented coffee vending machine that manages a catalogue of beverage recipes (espresso, latte, cappuccino, etc.), tracks ingredient inventory, and brews drinks on demand.

Core Use Cases

Select a beverage

User chooses from a menu of available coffee drinks (espresso, latte, cappuccino, etc.)

Customise a drink

User adjusts ingredient quantities — extra sugar, less milk, add cream

Brew and dispense

Machine prepares the drink by consuming ingredients per the recipe and dispensing it

Check ingredient availability

Before brewing, verify all ingredients are sufficiently stocked

Display available menu

Dynamically show only beverages that can be made with current stock

Refill ingredients

Admin restocks ingredients when they run low

Payment handling

Accept payment and return change before dispensing

Constraints

Each beverage is defined by a recipe — a fixed set of ingredients and their quantities
The machine has finite ingredient reservoirs with known capacities
A beverage can only be made if all required ingredients are sufficiently stocked
Customisations adjust ingredient quantities but cannot add ingredients not in the base recipe
Only one beverage can be brewed at a time (sequential processing)

Assumptions

Payment is simplified — assume exact payment or simple change return
No temperature or brewing-time simulation
Ingredient units are standardised (ml for liquids, grams for solids)
Recipes are pre-configured at startup by an admin

In Scope

Recipe management and beverage catalogue
Ingredient inventory tracking
Availability-based menu generation
Drink customisation within recipe bounds
Brewing workflow (select → pay → dispense)

Out of Scope

Actual hardware control (grinder, heater, pump)
Temperature and brewing-time simulation
Credit/debit card payment integration
Remote monitoring and IoT connectivity
Cup size and lid management

Approach Guide(Click to expand each section)

Before diving into code, clarify the use cases and edge cases. Understanding the problem deeply leads to better class design.

List Core Use Cases

Identify the primary actions users will perform. For a parking lot: park vehicle, exit vehicle, check availability. Each becomes a method.

Identify Actors

Who interacts with the system? Customers, admins, automated systems? Each actor type may need different interfaces.

Clarify Constraints

What are the limits? Max vehicles, supported vehicle types, payment methods. Constraints drive your data structures.

Ask About Edge Cases

What happens on overflow? Concurrent access? Payment failures? Thinking about edge cases reveals hidden complexity.

Follow-up Questions(Questions an interviewer might ask)

💡 Draw UML class diagrams, sequence diagrams, or any design visualizations. Submit from the Code tab.

Loading canvas...

Design a Coffee Vending Machine

Core Use Cases

Constraints

Assumptions

In Scope

Out of Scope

Approach Guide(Click to expand each section)

Follow-up Questions(Questions an interviewer might ask)

Explore the full editorial.

Sign in to view submissions

Design a Coffee Vending Machine

Core Use Cases

Constraints

Assumptions

In Scope

Out of Scope

Approach Guide(Click to expand each section)

Follow-up Questions(Questions an interviewer might ask)

Explore the full editorial.

Sign in to view submissions

Design a Coffee Vending Machine

Core Use Cases

Constraints

Assumptions

In Scope

Out of Scope

Approach Guide(Click to expand each section)

Gather Requirements~3 min

Identify Classes & Entities~4 min

Define Relationships~3 min

Apply Design Patterns~4 min

Apply SOLID Principles~3 min

Code Organization~2 min

Follow-up Questions(Questions an interviewer might ask)

1How would you support adding entirely new ingredients at runtime (e.g., oat milk)?

2How would you implement a recommendation engine that suggests drinks based on ingredient availability?

3How would you add combo deals (e.g., coffee + muffin)?

4How would you alert maintenance staff when an ingredient runs low?

Key Topics

Asked At

Explore the full editorial.

Sign in to view submissions

Design a Coffee Vending Machine

Core Use Cases

Constraints

Assumptions

In Scope

Out of Scope

Approach Guide(Click to expand each section)

Gather Requirements~3 min

Identify Classes & Entities~4 min

Define Relationships~3 min

Apply Design Patterns~4 min

Apply SOLID Principles~3 min

Code Organization~2 min

Follow-up Questions(Questions an interviewer might ask)

1How would you support adding entirely new ingredients at runtime (e.g., oat milk)?

2How would you implement a recommendation engine that suggests drinks based on ingredient availability?

3How would you add combo deals (e.g., coffee + muffin)?

4How would you alert maintenance staff when an ingredient runs low?

Key Topics

Asked At

Explore the full editorial.

Sign in to view submissions