State / Behavioral• Patterns: State, Singleton

Coffee Machine

Easy

Problem Summary

Design a Coffee Machine controller that selects recipes, validates ingredients inventory, accepts payments, and dispenses coffee.

Functional Scope

Support multiple recipes (Espresso, Latte, Cappuccino).
Check ingredients levels (water, milk, beans) before starting brew.
Lock machine during dispensing and update inventory levels.

Entity-Relationship (ER) Schema

CoffeeMachine [1] <---> [1] Inventory
CoffeeMachine [1] <---> [*] Recipe
Inventory [1] <---> [*] Ingredient

Design Approach

Represent structural recipes as immutable objects. Protect updates to the shared ingredients map using synchronized blocks or concurrent maps.

Core Classes & Models

CoffeeMachine (Context)CoffeeState (Idle, CheckingInventory, Dispensing, RefillNeeded)Recipe (Coffee beans weight, milk vol, water vol, cost)

Code Blueprint

public class CoffeeMachine {
    private Map<String, Integer> inventory = new ConcurrentHashMap<>();
    public synchronized boolean checkIngredients(Recipe r) { return true; }
}