Problem Set 6: Vending Machine

Task Outline

• Due Date: Wednesday, October 23, 2019
• Total Points: 10
• Implement a Java program that dispenses the correct amount of change, depending on the stock of coins in the machine.

Background Theory

• You will write a program that simulates the behaviour of a coin-operated vending machine, a device that was in common use until recently.
• A vending machine operates as follows: A customer selects an item for purchase, then inserts a certain amount of cash to cover the cost of the item. The product is then dispensed, and if change is due to the customer, it is provided in the form of coins.
• The vending machine we will consider has a finite stock of the following coins: 25 cents(quarters), 10 cents(dimes), and five cents(nickels). Note that pennies will be excluded from consideration.
• The amount of change due to a customer is calculated according to the following simple relation: change = payment - cost.
• The vending machine should then dispense the minimum quantity of coins necessary to provide the change to the customer.
• However, what would happen if the machine completely ran out of a particular coin denomination, for instance, the quarter? In that case, the machine would have to fulfill its obligation by using its remaining stock of dimes and nickels.
• Note that the output of this program should be the quantity of coins that are dispensed by the vending machine.

Example Case

• Consider the case where a customer deposits 200 cents into a vending machine, to purchase a product costing 70 cents. The change due to the customer is 130 cents.
• Then, let's say that the vending machine has a coin stock of 3 quarters, 3 dimes and 10 nickels.
• The vending machine will then dispense 3 quarters, 3 dimes and 5 nickels to the customer, which is 11 coins in total. Your program should return 11 as its result.

Hints

• Assume that the customer always deposits paper currency as payment. In other words, the payment placed into the vending machine does not replenish the coin stocks.
• Every time you dispense a coin to the customer, reduce that coin stock by one.
• The cost of the products, and the payment deposited, are all denominated in cents. This greatly simplifies the programming involved.
• You must calculate the minimum quantity of coins possible to fulfill the amount of change due to the customer.
• We won't consider the case where the vending machine has an insufficient stock of coins to cover the amount of change due to the customer. There will always be enough coins in each case.

Code Distribution

Description	File Size	File Name
Java Source Code for Vending Machine	4.9KB	pset06.zip

Contents of pset06.zip:

PSet06VendingMachine/
├── package.bluej
├── README.TXT
├── VendingMachine.class
├── VendingMachine.ctxt
├── VendingMachine.java
├── VendingMachineJUnitTest.class
├── VendingMachineJUnitTest.ctxt
└── VendingMachineJUnitTest.java

Specification

• Write a Java program in the file VendingMachine.java that dispenses the correct amount of change, depending on the stock of coins in the machine.
• You will write your solution in a function called dispenseChange(int quarters, int dimes, int nickels, int cost, int payment) right below the place where it says: YOUR CODE HERE
• When the function call dispenseChange(5, 5, 5, 160, 200) is executed, the output of the program should be: 3

Testing

• Click on the Run Tests button to execute the JUnit test bench. JUnit indicates a successful test with a green bar, and an unsuccessful test with a red bar.

Submission

• Upload the file VendingMachine.java to the Web-CAT automated grading platform.