Vending Machine — Notes

Functional

• Browse items, select.
• Accept cash or card / UPI.
• Make change.
• Dispense item.
• Refund on cancel.

Non-functional

• Reliable state transitions; never charge without dispense.
• Refill / maintenance mode.

Patterns

• State, Strategy (payment), Singleton (machine), Observer (low stock).

Trade-offs

• Multiple payment methods complicate state; isolate per PaymentMethod.
• No change available → reject coin or reduce options.

Refs

• Common LLD references (Grokking OOD).