How should date properties be defined in a java class?

Question

I have a simple java object with several date properties and I always seem to change my mind on how to define them. Should the properties be defined as date objects or strings? The object is going to be used in struts 1.3 application with iBatis as the persistence layer and mysql as the database. The database columns are defined as datetime and they can possibly be null and I usually don’t care about the time portion.

public Date getForcastDate();

or

public String getForcastDate();

Most of the existing code base uses strings, but that just doesn’t seem quite right to me.

Answer 1

Keep your dates as Dates. That way you can change formatting depending on locales, check for invalid dates, sort by them etc.

By keeping them as strings you're potentially throwing away data (e.g. milliseconds if your formatter doesn't use them) and definitely behaviour.

Using strong-typing (e.g. keeping them as Dates) will aid in terms of development. Your method signatures become clearer, refactoring using IDE tooling becomes easier etc. Otherwise you end up with APIs that talk in nothing but strings, it's trivial to mix up parameters, and it becomes impossible to work out what's going on.

Tip: Check out Joda-Time as a better alternative to the standard java.util.Date.

Answer 2

I would use Date object because it cleaner to store a Date and convert it to a String when needed. Otherwise you have to hard code a formatted date into a String field.