Best way to define true, false, unset state

Question

If you have a situation where you need to know where a boolean value wasn't set (for example if that unset value should inherit from a parent value) the Java boolean primitive (and the equivalent in other languages) is clearly not adequate.

What's the best practice to achieve this? Define a new simple class that is capable of expressing all three states or use the Java Boolean class and use null to indicate the unset state?

Answer 1

Boolean a = true; Boolean b = false; Boolean c = null; 

I would use that. It's the most straight-forward.

Another way is to use an enumeration. Maybe that's even better and faster, since no boxing is required:

public enum ThreeState {     TRUE,     FALSE,     TRALSE }; 

There is the advantage of the first that users of your class doesn't need to care about your three-state boolean. They can still pass true and false. If you don't like the null, since it's telling rather little about its meaning here, you can still make a public static final Boolean tralse = null; in your class.