Designing a coffee machine

I was recently rejected from what looked like a really promising string of interviews. I did very well in a questionnaire style review, and then they handed me this assignment (more or less):


Design a coffee machine which makes different beverages based on set ingredients. The initialization of the recipes for each drink should be hard-coded, although it should be relatively easy to add new drinks. The machine should display the ingredient stock (+cost) and menu upon startup, and after every piece of valid user input. Drink cost is determined by the combination of ingredients. For example, Coffee is 3 units of coffee (75 cents per), 1 unit of sugar (25 cents per), 1 unit of cream (25 cents per). Ingredients and Menu items should be printed in alphabetical order. If the drink is out of stock, it should print accordingly. If the drink is in stock, it should print "Dispensing: ". To select a drink, the user should input a relevant number. If they submit "r" or "R" the ingredients should restock, and "q" or "Q" should quit. Blank lines should be ignored, and invalid input should print an invalid input message.

They supplied the default ingredients (&stock @10) and drinks/recipes.

They told me to "not try and impress", don't overly document (specifically commenting is not required). The code should be scaleable, readable, and just not overly complicated.

Anyway, it's more likely that I made some major error in data structure choice or handling drink selections, than me missing some detail. Still, I can privately send the full assignment description if anyone is curious...I just don't want to put it out there since it's a big company currently hiring. I changed the name of some stuff in my code to make the exact assignment less searchable. I actually have a lot of opinions on things I would change in this code, but I have a hard time believing that they are things that would get me rejected. It must be something bigger...

(I have since been informed that the team

I have since been informed that the team was hoping for "A more OO design"...felt like I took it in that direction, personally.

All the methods in your DrinkMachine class are static. I believe the ability to have more than one DrinkMachine is a very important feature. DrinkMachines should be able to have different inventories, different products, etc. Now, you might think "But I was told to keep it simple!". This is not about "trying to impress" or anything, this is about reasonable functionality.

I am afraid that this staticness of the DrinkMachine cost you a lot of "interview-points".

Do you really need to be able to change the name of an Ingredient after it has been created?

I think you should strive on making some of your fields final. This also helps with tim's point about you don't need to initialize fields if you assign them in a constructor, that's just confusing. - final fields can only be initialized once.

StackExchange Code Review Q#83135, answer score: 35