Design and implement (in Java) a program that simulates a vending machine. Produ
ID: 3586464 • Letter: D
Question
Design and implement (in Java) a program that simulates a vending machine. Products can be purchased by inserting the correct number of coins into the machine. A user selects a product from a list of available products, adds coins, and either gets the product or gets the coins returned if insufficient money was supplied or if the product is sold out. Products can be restocked and money removed by an operator..
Remaining 50% is based on the elegance of your design with respect to classes and their interactions. I'll be evaluating this based on the code itself (not asking for any other class documentation such as CRC cards, etc.), but you're more likely to arrive at a good class design if you follow the process.
Explanation / Answer
The public API of vending machine, usually all high-level functionality should go in this class.
VendingMachine.java
package vending;
import java.util.List; /* Decleare public API for Vending Machine */
public interface VendingMachine {
public long selectItemAndGetPrice(Item item);
public void insertCoin(Coin coin);
public List<Coin> refund();
public Bucket<Item,List<Coin>> collectItemAndChange();
public void reset();
}
Vending machine implementation can be done as:
VendingMachineImpl.java
package vending;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/*
Sample implementation of Vending Machine in Jav
*/
public class VendingMachineImpl implements VendingMachine
{
private Inventory<Coin> cashInventory = new Inventory<Coin>();
private Inventory<Item> itemInventory = new Inventory<Item>();
private long totalSales;
private Item currentItem;
private long currentBalance;
public VendingMachineImpl()
{
initialize();
}
private void initialize(){
//initialize machine with 5 coins of each denomination
//and 5 cans of each Item
for(Coin c : Coin.values())
{
cashInventory.put(c, 5);
}
for(Item i : Item.values())
{
itemInventory.put(i, 5);
}
}
public long selectItemAndGetPrice(Item item)
{
if(itemInventory.hasItem(item))
{
currentItem = item;
return currentItem.getPrice();
}
throw new SoldOutException("Sold Out, Please buy another item");
}
public void insertCoin(Coin coin)
{
currentBalance = currentBalance + coin.getDenomination();
cashInventory.add(coin);
}
public Bucket<Item, List<Coin>> collectItemAndChange()
{
Item item = collectItem();
totalSales = totalSales + currentItem.getPrice();
List<Coin> change = collectChange();
return new Bucket<Item, List<Coin>>(item, change);
}
private Item collectItem() throws NotSufficientChangeException,
NotFullPaidException
{
if(isFullPaid())
{
if(hasSufficientChange())
{
itemInventory.deduct(currentItem);
return currentItem;
}
throw new NotSufficientChangeException("Not Sufficient change in
Inventory");
}
long remainingBalance = currentItem.getPrice() - currentBalance;
throw new NotFullPaidException("Price not full paid, remaining : ",
remainingBalance);
}
private List<Coin> collectChange()
{
long changeAmount = currentBalance - currentItem.getPrice();
List<Coin> change = getChange(changeAmount);
updateCashInventory(change);
currentBalance = 0;
currentItem = null;
return change;
}
public List<Coin> refund()
{
List<Coin> refund = getChange(currentBalance);
updateCashInventory(refund);
currentBalance = 0;
currentItem = null;
return refund;
}
private boolean isFullPaid()
{
if(currentBalance >= currentItem.getPrice())
{
return true;
}
return false;
}
private List<Coin> getChange(long amount) throws NotSufficientChangeException
{
List<Coin> changes = Collections.EMPTY_LIST;
if(amount > 0)
{
changes = new ArrayList<Coin>();
long balance = amount;
while(balance > 0)
{
if(balance >= Coin.QUARTER.getDenomination()
&& cashInventory.hasItem(Coin.QUARTER))
{
changes.add(Coin.QUARTER);
balance = balance - Coin.QUARTER.getDenomination();
continue;
}
else if(balance >= Coin.DIME.getDenomination()
&& cashInventory.hasItem(Coin.DIME))
{
changes.add(Coin.DIME);
balance = balance - Coin.DIME.getDenomination();
continue;
}
else if(balance >= Coin.NICKLE.getDenomination()
&& cashInventory.hasItem(Coin.NICKLE))
{
changes.add(Coin.NICKLE);
balance = balance - Coin.NICKLE.getDenomination();
continue;
}else if(balance >= Coin.PENNY.getDenomination()
&& cashInventory.hasItem(Coin.PENNY))
{
changes.add(Coin.PENNY);
balance = balance - Coin.PENNY.getDenomination();
continue;
}
Else
{
throw new NotSufficientChangeException("NotSufficientChange,
Please try another product");
}
}
}
return changes;
}
public void reset()
{
cashInventory.clear();
itemInventory.clear();
totalSales = 0;
currentItem = null;
currentBalance = 0;
}
public void printStats()
{
System.out.println("Total Sales : " + totalSales);
System.out.println("Current Item Inventory : " + itemInventory);
System.out.println("Current Cash Inventory : " + cashInventory);
}
private boolean hasSufficientChange()
{
return hasSufficientChangeForAmount(currentBalance - currentItem.getPrice());
}
private boolean hasSufficientChangeForAmount(long amount)
{
boolean hasChange = true;
try
{
getChange(amount);
}
catch(NotSufficientChangeException nsce){
return hasChange = false;
}
return hasChange;
}
private void updateCashInventory(List change)
{
for(Coin c : change)
{
cashInventory.deduct(c);
}
}
public long getTotalSales()
{
return totalSales;
}
}
VendingMachineFactory.java
A factory class to create different kinds of vending machines.
package vending;
/* Factory class to create instance of Vending Machine, this can be extended to create instance of * different types of vending machines.*/
public class VendingMachineFactory
{
public static VendingMachine createVendingMachine()
{
return new VendingMachineImpl();
}
}
Item.java
Java enum to represent item served by vending machine.
package vending;
/*
Items or products supported by Vending Machine.
*/
public enum Item
{
COKE("Coke", 25), PEPSI("Pepsi", 35), SODA("Soda", 45);
private String name;
private int price;
private Item(String name, int price)
{
this.name = name;
this.price = price;
}
public String getName()
{
return name;
}
public long getPrice()
{
return price;
}
}
Coin.java
Another Java Enum to represent Coins supported by Vending Machine
package vending;
/** Coins supported by Vending Machine. */
public enum Coin
{
PENNY(1), NICKLE(5), DIME(10), QUARTER(25);
private int denomination; private Coin(int denomination)
{
this.denomination = denomination;
}
public int getDenomination()
{
return denomination;
}
}
Inventory.java
A Java class to represent an Inventory, used for creating case and item inventory inside Vending Machine.
package vending;
import java.util.HashMap;
import java.util.Map;
/*
* An Adapter over Map to create Inventory to hold cash and
* Items inside Vending Machine
*/
public class Inventory<T> {
private Map<T, Integer> inventory = new HashMap<T, Integer>();
public int getQuantity(T item){
Integer value = inventory.get(item);
return value == null? 0 : value ;
}
public void add(T item){
int count = inventory.get(item);
inventory.put(item, count+1);
}
public void deduct(T item) {
if (hasItem(item)) {
int count = inventory.get(item);
inventory.put(item, count - 1);
}
}
public boolean hasItem(T item){
return getQuantity(item) > 0;
}
public void clear(){
inventory.clear();
}
public void put(T item, int quantity) {
inventory.put(item, quantity);
}
}
Bucket.java
A parameterized utility class to hold two objects.
package vending;
/* A parameterized utility class to hold two different object. * /
public class Bucket<E1, E2>
{
private E1 first; private E2 second; public Bucket(E1 first, E2 second)
{
this.first = first; this.second = second;
}
public E1 getFirst()
{
return first;
}
public E2 getSecond()
{
return second;
}
}
NotFullPaidException.java
An Exception, thrown by Vending Machine when a user tries to collect an item, without paying the full amount.
package vending;
public class NotFullPaidException extends RuntimeException {
private String message;
private long remaining;
public NotFullPaidException(String message, long remaining) {
this.message = message;
this.remaining = remaining;
}
public long getRemaining(){
return remaining;
}
public String getMessage(){
return message + remaining;
}
}
NotSufficientChangeException.java
Vending Machine throws this exception to indicate that it doesn't have sufficient change to complete this request.
package vending;
public class NotSufficientChangeException extends RuntimeException {
private String message;
public NotSufficientChangeException(String string)
{
this.message = string;
}
public String getMessage()
{
return message;
}
}
SoldOutException.java
The Vending Machine throws this exception if the user request for a product which is sold out.
package vending;
public class SoldOutException extends RuntimeException {
private String message;
public SoldOutException(String string)
{
this.message = string;
}
public String getMessage(){
return message;
}
}
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