Processing 1.0 - Processing Discourse - Static Fields & Methods in Non-Static Class

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Index › Programming Questions & Help › Syntax Questions › Static Fields & Methods in Non-Static Class

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Static Fields & Methods in Non-Static Class (Read 583 times)

AndyB

Static Fields & Methods in Non-Static Class
Feb 7^th, 2009, 2:54am

Example: the classic singleton pattern.

Code:

public class Singleton {
   private static Singleton instance = null;
   protected Singleton () { }
   public static Singleton getInstance() {
	     if(instance == null) { instance = new Singleton(); }
	     return instance;
   }
}

Processing responds to this with the message, "The field instance cannot be declared static; static fields can only be declared in static or top level types."

Is there any reason why the ENTIRE class is required to be static? Is there any way around this restriction?

PhiLho

Re: Static Fields & Methods in Non-Static Clas
Reply #1 - Feb 7^th, 2009, 11:13am

All code in a .pde file (and other .pde files in the same sketch) is gathered into a single class named along the name of the sketch.
It is convenient in general, and works well in most cases, as classes can be nested, global variables are actually fields of the invisible enclosing class, etc.

But Java introduce limitations like restrictions on static stuff and no interfaces there.

To avoid this problem, Processing allows to put .java files in the sketch as well: they will be compiled to .class files independently of the main class. That's what you need.
The only catch is that you don't have the Processing functions available there, unless you pass an instance of the main class to them.

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