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Design an object-oriented vending machine system that handles product selection, money insertion, dispensing, and change calculation.
The machine should use a state-based lifecycle (idle → has money → dispensing) to manage transactions cleanly, support inventory tracking, and return the correct change using available denominations.
Insert money
Accept coins and notes; accumulate the current balance
Select a product
User picks a product by its code from the display grid
Dispense product
Release the product if the balance covers the price
Return change
Compute and return the correct change using available denominations
Cancel transaction
Refund all inserted money and reset to idle
Manage inventory
Admin can restock products and update prices
Display product info
Show available products, prices, and stock status
Before diving into code, clarify the use cases and edge cases. Understanding the problem deeply leads to better class design.
Identify the primary actions users will perform. For a parking lot: park vehicle, exit vehicle, check availability. Each becomes a method.
Who interacts with the system? Customers, admins, automated systems? Each actor type may need different interfaces.
What are the limits? Max vehicles, supported vehicle types, payment methods. Constraints drive your data structures.
What happens on overflow? Concurrent access? Payment failures? Thinking about edge cases reveals hidden complexity.
The complete explanation is included with Career and All Access. Compare it with your approach once you’ve worked through the problem.