So the company I work for asked me to come up with a suitable problem that can be handed to candidates prior to their coming in for an on-site interview. Against my urging, there was a two hour time limit placed on implementing the solution. At the time, I decided to do the exercise myself, as a feasibility check on the problem restrictions and scope, and that effort is the contents of this repository.
This was completed in the two hour time limit. I have not modified the code after that, so it shows the state with that amount of effort. I have gone back and done a self-critique, which you can find as in-line comments in the code.
Note that since then, managment took my advice and changed it to an overnight coding exercise.
Design the domain model for an object oriented vending machine that can handle different products, can accept payments, and can vend product. Do not model an interactive menu loop! Given that this is a limited interview question, you can limit the level of detail that you model at.
There are some featues you would expect to see in a productized version of this code, which are not here:
- Use of dependency injection (Spring or better yet Guice)
- Use of multi-threading to account for menuing and controller activity
- More detailed breakdown of behavior at the level of individual buttons
- Use of events and states as a more abstract means of managing behavior
- Use a package heirarchy and production/test folder structure
The best place to start is with VendingMachineTest.
Design of a vending machine is a common interview-related problem. The point of this is to demonstrate some minimal knowledge of abstraction and design. This is the chance for the candidate to showcase their coding prowess.
In my solution, there are some design, best practices, and software quality points that are captured as comments so you'll have to scan the code. None of the code was developed using TDD; in a timed interview situation like this, it is not appropriate (unless stated as part of the requirements).
Compare this solution to some found on the web like those below that tend to focus on mastery of the language, yet exhibit inferior design. My solution is not the only way to design for this problem. For example, if the problem is more at a hardware controller level where there are more detailed inputs and responses required, say modeling of individual button presses, you might use a state machine to capture the internal behavior.
http://www.daniweb.com/software-development/java/threads/179994/java-vending-machine-program
http://www.coderanch.com/t/621654/java/java/Vending-Machine-Assignment