VendingMachine

The class VendingMachine can be used to simulate simple virtual soda vending machines. A vending machine sells bottles of a single type of soft drink at a certain price per bottle.

The methods of the class correspond to the actions of buyers and maintenance personnel on an actual vending machine. For instance, a purchase is made by first inserting some money possibly several times with each one adding to the previous insertion, and then selecting to buy a bottle. This interaction is captured by the methods insertMoney and buyBottle.

Some of the methods are illustrated in the following REPL session, in which the vending machine initially contains 10 bottles with a price of 250 cents (2.5 euros) each:

scala> val machine = VendingMachine(250, 10)
machine: o1.soda.VendingMachine = earned 0.0 euros, inserted 0 cents, 10 bottles left

scala> machine.insertMoney(300)

scala> "got change: " + machine.sellBottle()
val res0: String = got change: 50

scala> machine
val res1: o1.soda.VendingMachine = earned 2.5 euros, inserted 0 cents, 9 bottles left

scala> machine.insertMoney(50)

scala> machine.insertMoney(300)

scala> machine.sellBottle()
val res2: Int = 100

scala> machine
val res3: o1.soda.VendingMachine = earned 5.0 euros, inserted 0 cents, 8 bottles left

As the example illustrates, a vending machine object has a mutable state: it keeps track of how much money the user has inserted, for instance. The machine also tracks the number of bottles it contains, the current (modifiable) price per bottle, and the money it has “earned” by selling bottles.