Vending Machine Low Level System Design

User Flow diagram of vending machine

Interfaces:

these interfaces contains all the possible state of the vending machine.

public interface CoinHandler {    

public void insertCoin(Coin coin);

}

public interface ItemDispenser {    

void dispenseItem(Item item, int quantity);

}

public interface ItemSelector {    

public void selectItem(Item item, int quantity);

}

public interface TransactionHandler {    

void cancel();    

void refund();

}

State class which are implementing these interfaces

NoCoinState Class: this is an idea state of vending machine, and this state only support insert coin feature.

HasCoinState Class: this is the second stage , when user enters coin then user can select item and quantity of the item.

In this stage user can cancel the process and well and get the refund

ItemSelectedState Class: this is a third stage of a vending machine, when user enters coin and selected the item then user can dispatch the item

Coin Enum: this is a simple coin enum

Item Class: here we can add the items

Inventory Class: this class is used to manage the item of a vending machine so that we can easily track the items availability

Vending Machine State: class to manage current state value of a vending machine, i.e how much balance has been inserted and what item is selected and the what are the coins

Class Vending Machine: this class have all the other classes using that we can perform all the tasks of vending machine

Main class: to test the all code

Please feel free to suggest your opinion

Happy Coding !!