Null/not set

Question

hi, I'm writing some code where I want to draw a distinction between a variable being 'blank' (ie has been set to empty) and 'not set' (hasn't been set to anything).
In a database you could say a value is 'null' or 'not set', but in java I suspect that null actually means 'not set'. (Is this getting confusing?)
so I'd like to be able to do this:
bob.setSurname(null); // bob has no surname
bob.setTitle(blank); // bob has a title, and that title is ""
I imagine this is impossible because null is a reserved word that java does something special with (?)
My setTitle method is expecting a String so I could create a blankString string object to pass to it. Only problem then is that I have to create blankInteger and blankDate and so on. Doesn't seem like a very elegant solution to me... I could create my own String class with a 'setEmpty()' method on it, but then I might as well be writing in C++ ;-)
Does anyone have any better suggestions?

Answer 1

hi, I'm writing some code where I want to draw a
distinction between a variable being 'blank' (ie has
been set to empty) and 'not set' (hasn't been set
to anything).This vexes many SQL programmers, too. Does NULL mean that there is no value, or that it's unknown, or it hasn't been initialized yet, or isn't applicable, or ...?
In Java, the null reference is a value that indicates that the reference does not point to an object. You have to decide what semantics to give that value. If you want null to indicate that the value hasn't been set, you need an object to indicate that the value has been set to "blank".
In the case of a String, you could make a special String object:
public final BLANK_VALUE = new String();
and then use == to test for this object. Often, however, the empty String "" is used to indicate the value has been set to "blank".