How to tell Processing that the value is undefined?

djevazi

How to tell Processing something like this: if the value is defined then do this, but if the value is undefined then do that ?

jeremydouglass

What value, specifically? Is this a Processing built-in object like PVector, or your own custom class object, or a string...? It depends -- for example, data primitives like int have a default value when they are declared, even if they are not initialized, so the approach you are describing wouldn't work for an int.

int i;
println(i): // prints 0

djevazi

Sorry, maybe I got to write some code example, and then ask this question again, because now even I don't understand what I really meant : )

koogs

using null for undefined objects is a common thing in java - you often see snippets of code like

if (str != null) {
  println("Length:", str.length());
}

mostly this is to protect calling methods on a undefined object, which will cause a null pointer exception.

(this doesn't work for primitive types like int or float, but does for Objects like String, or indeed, Integer)

GoToLoop

• In Java by default, everything is defined before compilation.
• Although we can use reflection techniques in order to check whether some particular member exists in an object.
• However, we can also dynamically add & remove members from an object if we use some script language module.

djevazi

Thanks, maybe "null" is what i needed. It is sad that not working with int and float. What is the difference between int and Integer? I don't even see Integer in processing reference category.

GoToLoop

• Class Integer is a wrapper for 1 int value.
• It also includes a buncha util methods & constants, most of them static:
  http://docs.Oracle.com/javase/8/docs/api/java/lang/Integer.html
• Obviously it's slightly slower & wastes more RAM than a raw primitive int. 3:-O

djevazi

thanks!

jeremydouglass

For many designs it not necessary to use Integer rather than int just to have something nullable. You also have other options:

1. Assign value(s) to an array or ArrayList or IntList, and check the length of the list to see whether a particular value has been assigned.
2. For a single value, use a separate boolean as a guard field (e.g. isDefined).
3. Depending on the use of the variable, use a natural value in the primitive itself to indicate non-assignment. For example, if you are only using the positive range of a signed int, -1 could mean "unassigned." Or use a non-operative value -- for example, if your int is a scaling factor, 1 does nothing; if your int is additive, 0 does nothing.

GoToLoop

3) Depending on the use of the variable, use a natural value in the primitive itself to indicate non-assignment.

I've done that already. My fav value for it is MIN_INT. $-)

djevazi

many useful tips, thanks, people.

Eeyorelife

I suspect that this is only true for javascript, but Daniel Shiffman is often blown away by how good javascript is to just turn everything into true or false.

I bet that in javascript you can have an undefined or defined var "man" and ask if(man) {//do something}, and it will automatically conside whether or not "man" is undefined or defined even if it holds an integer or a float.

But don't quote me on that, you'll need to try it. It might also work with java.

GoToLoop

https://developer.Mozilla.org/en-US/docs/Glossary/Truthy