Coffee Vending Machine (LLD - Java)

This repository contains a Low Level Design (LLD) implementation of a Coffee Vending Machine in Java.

It supports:

• Displaying a menu of available coffees
• Multiple coffee types (Espresso, Cappuccino, Latte)
• Each coffee having a price and an ingredient recipe
• Adding extras (milk / sugar / chocolate syrup) using the Decorator pattern
• Inventory management for ingredient availability
• Payment flow with multiple money insertions
• A vending-machine State Machine (Ready → Selected → Paid)

---

Requirements Coverage

1) Menu to display available items

• Implemented in: src/CoffeeVendingMachine/CoffeeMachine.java
• Method: displayMenu()
• It iterates over CofeeTypes and prints the base coffee price.

2) Different types of coffees (Espresso, Cappuccino, Latte)

• Implemented in:
  • src/CoffeeVendingMachine/Coffee/Espresso.java
  • src/CoffeeVendingMachine/Coffee/Cappuccino.java
  • src/CoffeeVendingMachine/Coffee/Latte.java
• Creation via factory:
  • src/CoffeeVendingMachine/Factory/CoffeeFactory.java

3) Each coffee has price and ingredients

• Interface:
  • src/CoffeeVendingMachine/Coffee/Coffee.java
• Contract:
  • Integer getPrice()
  • Map<Ingredients, Integer> getRecipe()

4) Each coffee has a specific ingredient percentage

Recipes are represented as a Map<Ingredients, Integer>.

In the current code, these integers are used as ratio/percentage-like weights.

• Cappuccino and Latte recipes sum to 100.
• Espresso currently sums to 80 (this can be adjusted to 100 if you want strict “must sum to 100” percentage enforcement).

Ingredient enum:

• src/CoffeeVendingMachine/Enums/Ingredients.java

5) Decorations (extras) should be able to add to existing coffee

Extras are implemented using the Decorator Pattern.

• Base decorator:
  • src/CoffeeVendingMachine/Decorators/BaseDecorator.java
• Extras:
  • MilkDecorator
  • SugarDecorator
  • ChocolateSyrupDecorator

Each decorator updates:

• getDescription() (adds extra text)
• getPrice() (adds extra cost)
• getRecipe() (adds extra ingredient requirement)

Example:

Coffee cappuccino = CoffeeFactory.getCoffee(CofeeTypes.CAPPUCCINO);
Coffee cappuccinoWithChoco = new ChocolateSyrupDecorator(cappuccino);

6) Inventory management (ingredient availability tracking)

• Implemented in: src/CoffeeVendingMachine/Inventory.java

Key methods:

• addIngredient(ingredient, amount)
• hasIngredients(recipe)
• deductIngredient(recipe)

If the recipe cannot be fulfilled, the machine throws:

• src/CoffeeVendingMachine/Exceptions/InsufficientIngredientsException.java

7) Payment support (multiple money insertions)

The machine supports inserting money multiple times until the total meets/exceeds the coffee price.

• State implementation:
  • src/CoffeeVendingMachine/State/SelectedState.java

Important behavior:

• insertMoney(amount) accumulates money:
  • machine.setInsertedMoney(machine.getInsertedMoney() + amount);
• Only when the total inserted money ≥ price does it move to PaidState.

8) CoffeeVendingMachine states (ready, select, payment)

State pattern is implemented in:

• src/CoffeeVendingMachine/State/VendingMachineState.java

Concrete states:

• ReadyState → allows selecting coffee (also checks inventory)
• SelectedState → accepts money insertion(s)
• PaidState → dispenses and deducts inventory, returns change if any

State transitions happen inside CoffeeMachine through:

• selectCoffee(...)
• insertMoney(...)
• dispense()
• cancel()

---

How to Run

From the repository root:

javac $(find src -name '*.java')
java -cp src CoffeeVendingMachine.CoffeeVendingMachineDemo

Demo entry point:

• src/CoffeeVendingMachine/CoffeeVendingMachineDemo.java

---

Project Structure (High Level)

src/CoffeeVendingMachine/
  CoffeeMachine.java                 # Main machine (singleton) + menu
  Inventory.java                     # Ingredient stock management
  Coffee/                            # Coffee types + Coffee interface
  Decorators/                        # Add-ons using Decorator pattern
  Factory/                           # CoffeeFactory
  State/                             # State pattern (Ready/Selected/Paid)
  Enums/                             # CofeeTypes, Ingredients
  Exceptions/                        # InsufficientIngredientsException

---

Notes / Possible Enhancements

• Strict percentage enforcement: add recipe validation so every coffee recipe must sum to 100.
• Menu improvements: print recipes/ingredients in the menu output.