JavaFX's null not allowed is a thorn in my side....

Question

Hi All,
Rule: JavaFX's data types (i.e. Number, Double, String, Integer) can't be null.
My JavaFX Application listen's for real time data updates. Since this is a listener, it won't have a value til it get's the first update. Sounds fair enough... but they can't be null! So, I must use java.lang.Double instead. But all binding's convert the java.lang.Double null value to a javafx Double value of 0.0. So now I have broken logic in my program as 0.0 is a legitimate value and certainly does not signify 'null'. So, then it looks like I am stuck entirely with java.lang.Double everywhere! But then I'd need to do my own java.lang.Double -> fx.Double casting class/function to handle the cast conversion of each binding in order to interact sensibly with the JavaFX API (as it like's the FX Double everywhere and won't throw a nullpointer exception when casting).
Rule: JavaFX's sequences can't contain null entries.
Further more, I could say "Nope, I don't have a value/update yet so I will just use an object placeholder/wrapper with null assignment". In my case, JavaFX object's are multiple and ordered. Perfect for a sequence! Except, you can't store null in a sequence! Thus, if you are looking for a team's sport's top batsman.. the 3rd batsman and they don't exist yet.. then 'team[2] = null' wont insert! So how can I find and bind to the 3rd batsman? We'll either I avoid sequences, which means native array's or java collections... but then I can't really bind to them! Or, everytime the sequence changes I need to search/iterate over the entire sequence to determine if there is a 3rd batsman in the sequence (and that won't necessarily be the 3rd entry).
Both these 'null not allowed' rules cause significant problems and have huge flow on effects onto the code that uses them. I believe this is totally wrong and a bad feature of the language and completely contradicts autoboxing! The identification of a data type reference being null is extremely significant. It is the responsibility of the receiver of a null reference/argument to decided how they want to handle the null reference (see autoboxing nullpointer exceptions if you don't believe me and reasons not to use java primitives). Removing the ability for this to occur is a step backwards for functional programming. I know you will say that I could just use the java.lang.*, a fair claim... but don't forget this means more work! The very reason you might be considering JavaFX in the first place.
Anyway my rant is over, I really love JavaFX.... just not these x2 rules.

Answer 1

The technique PhiLho refers to is often called the "null object pattern". If done properly it needn't be hackish at all, and indeed it can simplify a lot of processing code. Even if the "primitive" values (Number, String, etc.) could be null, and even if you could put nulls into a sequence, you're probably better off putting in an actual object that represents the absence of a value. The reason is that when you go to process that data, instead of just processing it, you have to put in checks for nulls here and there, and do special-case processing for it.
Consider displaying a list of, say, the top five batsmen. You'll want to have a sequence of five batsmen, and you'll want to put five CustomNodes or something into a VBox to display the names, statistics, etc., something like the following:
VBox {
    content: [
        for (b in [0..<5]) {
            BatsmanNode {
                name: bind batsmen.name
innings: bind batsmen[i].innings
notOuts: bind batsmen[i].notOuts
visible: bind batsmen[i].valid
You can't do this if there were a null in the sequence, even if it were allowed. Instead, you should put a "fake" batsman object into the sequence, and make its "valid" variable be false. This way the corresponding BatsmanNode will be invisible. Or, you could have it display "(no entry)" in grey text, or something like that.
The point is that if you always have a real object there, even if it represents a "null" or the absence of a value, it removes special-case processing code and enables you to do things like bind to it.