CWI Date Operator

This project is a resolution of a code exam.

Problem definition

You should create the following function:

public String changeDate(String date, char op, long value);

Where,

• date: An date as String in the format “dd/MM/yyyy HH24:mi”;
• op: Can be only ‘+’ | ‘-‘;
• value: the value that should be incremented/decremented. It will be expressed in minutes;

Restrictions:

• You shall not work with non-native classes / libraries;
• You shall not make use of neither Date nor Calendar classes;
• If the op is not valid an exception must be thrown;
• If the value is smaller than zero, you should ignore its signal;
• If the result sum is bigger than max value to the field, you should increment its immediate bigger field;
• Ignore the fact that February have 28/29 days and always consider only 28 days;
• Ignore the daylight save time rules.

Example

changeDate("01/03/2010 23:00", '+', 4000) == "04/03/2010 17:40"

Design

Using inversion of control, immutability and dependency injection principles, I tried to design stateless objects to execute operations over immutable data objects.

To calculate the operation I used:

• DateOperator: stateless class that executes the operation
• Date: immutable POJO that represents a Date operated or to be operated
• Month: enumeration of time constants
• DateParser: parses the string into a Date object
• DateWriter: writes a Date object as the intended string output
• OperationValidator: validates the input operation
• DateValidator: validate if a given Date object is coherent
• MinutesDateConverter: converts a Date object to its minutes sum

Dependencies

• Java JDK version 1.7
• JUnit version 4.11
• Maven version 2.2
• Maven Compiler Plugin version 3.3