Cash Machine Back End Developer Position Test Task

A friendly reminder: If this repo somehow helped you please star 🌟 it! Thank you! 😄

Task

Is to create simple Cash Machine emulator.

Requirements (9/9 completed):

• create stand-alone console I/O Java program using any JDK;
• follow OOP paradigm;
• make program easily extendable;
• provide logging to the output file;
• divide program modules into packages;
• generate JavaDocs;
• write JUnit tests for public methods;
• make Ant build.xml;
• make functional test.

Input commands:

1. Cash deposit

Format: + <currency> <denomination> <amount>
Validation: 
* <currency> 3 uppercase letters, any combination
* <value> any value in set ["1","5","10","50","100","500","1000","5000"]
* <number> positive integer
Reply: OK on success, ERROR on validation fail

2. Cash withdraw

Format: - <currency> <amount>
Reply: line formatted as <denomination> <amount> followed by OK on success, ERROR if amount is unavailable

3. Cash print

 Format: ?
 Reply: OK, ordered by currency -> value

Run, build and test

Build

ant build

Test

ant test

Run

ant run

Solution

Before coding, we should make a plan:

1. How to handle commands;
2. Deposit/Withdraw strategy;
3. I/O common interface.

Commands handling

To handle the command problem I decided to go for behavioral design Command pattern which delegates command build to the command factory.

I recommend to check Jairo Alfaro's reply on StackOverflow since he gives a good example of the implementation in C#.

Deposit/Withdraw strategy

I decided to arrange data in a structure Map<String, TreeMap<Integer, Integer>> since we basically have this kind of structure:

Since we have to pop up bigger banknotes first, we store Map<Integer, Integer> in a reverse order. In Java, TreeMap<Integer, Integer> stores keys in a natural order, so in our case we should apply Collections.reverseOrder() on initialization.

The rest of the algorithm is a piece of cake. For the deposit we simply add cash to the denomination, for the withdrawal we subtract the amount of remove the denomination if the amount is exact. Also, handle the situation when amount is unavailable (denomination absence, etc.).

I/O common interface

I created an I/O interface (InputReader & OutputWriter) and implemented corresponding reader and writer to work with streams. These classes can work both with System.in/System.out and FileInputStream/FileOutputStream so we can easily switch between file and console I/O.