Comparing date by combining it - date

Question

Im just wondering. is it ok to combine years,month, and day of two date and make a comparison based on the combination.
eg:
Date A: 12th-January-2019
Date B: 24th-December-2018
Based on the above date, i could combine the year,month, and day as follow:
Date A: 20190112
Date B: 20181224
So based on the numbers, i could do logic like below to compare which date comes first:
if(Date A > Date B) {
output("Date A is the latest")
}
i would like to implement this method just to compare which is the latest date.
are there any problem of doing so.

Answer 1

java.time
Since you are using Java, I suggest that you take advantage of java.time, the modern Java date and time API.
String[] dateStringsFromDatabase = {
"2018/12/19",
"2017-02-01",
"2018.03.04",
"25-12-2016", // reversed
"2019\\09\\12",
"2014:03:01"
};
List<LocalDate> parsedDates = new ArrayList<>(dateStringsFromDatabase.length);
for (String dateString : dateStringsFromDatabase) {
// No matter which delimiter is used, replace it with a hyphen
String text = dateString.replaceAll("\\W", "-");
try {
parsedDates.add(LocalDate.parse(text));
} catch (DateTimeParseException dtpe) {
System.out.println(dateString + " not parsed: " + dtpe.getMessage());
}
}
Output:
25-12-2016 not parsed: Text '25-12-2016' could not be parsed at index 0
What this approach buys you is validation of the dates even though they come with all different delimiters. Especially in this situation I believe that you should want to validate that your strings are within the expected variations. Otherwise you risk that a date with the numbers reversed ends up as a date in year 2512, for example. You want to catch that before it happens.
Example of comparing which comes first:
for (int i = 1; i < parsedDates.size(); i++) {
LocalDate dateA = parsedDates.get(i - 1);
LocalDate dateB = parsedDates.get(i);
if (dateA.isAfter(dateB)) {
System.out.format("%s is later than %s%n", dateA, dateB);
}
}
Output:
2018-12-19 is later than 2017-02-01
2019-09-12 is later than 2014-03-01
Link: Oracle tutorial: Date Time explaining how to use java.time.