Best Way to Handle Blank Dates in Java

java

I'm trying to create a contact book application, and currently I'm working on a class called Person. One of the fields of person is dateOfBirth, however I don't know how to handle unknown dates. Until now I have been using java.time.LocalDate for dateOfBirth and I've been initialising the field to null at instantiation. This isn't ideal, because it's resulting in null pointer exceptions when I try to compare dateOfBirth to other dates such as the LocalDate.now().

What would be the best way to handle dateOfBirth? Should I just create an entirely new class and manage unknown dates internally? Or is ther some better way to do it. I was going to just extend LocalDate but it's immutable so can't be extended without going to the source.

Best Answer

Use the class `Optional<LocalDate>`

This useful container class was introduced in Java 8. It is a wrapper used for values which you might or might not know. It is unboxed with various methods which all allow you to handle the case that the value is unknown in a graceful manner.

get() unboxes the LocalDate, but throws a NoSuchElementException in case you have none. Unfortunately it is an unchecked exception, just like the dreaded NullPointerException. So I would recommend to avoid using this method and instead use:
orElseThrow(exception) which throws said exception when you don't have a value. The exception can (and should be) a checked exception so you are forced to handle it. Don't feel like writing a clunky try...catch... construct? In that case:
ifPresent(Consumer<? super T> consumer) is a useful construct when you want to execute some code only if you have a value and otherwise do nothing.
orElse(T value) unboxes the value but gets you the dummy value you provide when you have none

For more information, check the article "Tired of Null Pointer Exceptions? Consider Using Java SE 8's Optional!" on Oracle Tech Net and the documentation to see what other methods it provides.

Not using Java 8 yet?

When you are still using an older version of Java, you could easily improvise your own OptionalDate class, which has just:

private LocalDate
public void set(LocalDate value) and
public LocalDate get() throws DateUnknownException

By having the getter throw a checked exception you are forced to always handle the null-case.

Related Solutions

Java – the best way to handle nuances for different platforms

For the example you gave (file paths), you should use a configuration file. You can have one for each platform, or one big one with settings for all platforms. I'd lean toward the first option, because then you can just use that one file and all the paths would be set. Java has a rich set of methods to construct platform independent file paths; use things like File.separator rather than \.

Generally in Java you don't need to have separate projects for separate platforms - that's why the JVM! Use specific components for only those parts of the application that are platform specific. In my experience, I have not seen anything in Java intself that needs to change for different platforms. Interacting with the filesystem is trickier, but there are ways around that as described above. That being said, you should still test on the platforms you intend to deploy on to be sure that everything does work - sometimes there are subtle differences in JVMs for specialized applications.

My recommendation for jars and other platform specific components is to have a directory structure look something like this in your VCS:

/src
/lib
   linux/
      jars/
      config/
   windows/
      jars/
      config/

Then in your build scripts, only include the folder you need for the platform you're building for. I'd include the folder as lib in your build, so for a Linux build you'd end up with (as a suggestion):

/
*yourjar*
*launchfiles*
/lib
   jars/
   config/

Zip that whole thing up and unzip it where you want to install. That will avoid having to specify paths more than once in code at the expense of a slighly more complicated build process. You could probably put that in a windows installer, too.

Java Design – How to Handle Nested Collections More Elegantly

Create a class Triple with fields for A,B,Integer, override hashCode() and equals(), and use Map<Triple,C> instead of Map<A,Map<B,Map<Integer,C>>>

In this approach - you put all elements in one map, with a larger possible range of keys.