Question: How to change the default icon of my Processing `appIconTest.exe` exported 
application in windows ? 

**The default one :**

[![app icon to change](https://i.stack.imgur.com/u114Y.png)](https://i.stack.imgur.com/u114Y.png)

Answer: 
After some research, the easiest solution i could find is :

1. Go into `...\processing-3.0.1-windows64\processing-3.0.1\modes\java\application`
2. Save `sketch.ico` somewhere you can find (renaming it will help).
3. Place the icon you want to use in the same folder with the same name `sketch.ico` (which you might create using [GIMP](https://www.gimp.org/)).
4. Now you can export your application from Processing.

---

**Important :** Be sure to save the default icon, because every application you export (after changing the icon) using Processing, will have this new icon.
You can change the icon of your running application (the icon that shows up in the title bar of the window and the task bar), but I don't think that's what you're asking about. You can't easily change the icon of the file itself.

That icon seems to be coming from the `core.jar` Processing library file, so if you want to hack at it, you could try replacing that file in the jar. I really don't recommend that though.

Because the `.exe` file that Processing exports isn't really an executable anyway- it's really just a shell that calls the code in the `lib` directory. ([source](https://github.com/processing/processing/wiki/Export-Info-and-Tips))

If you want to create a real `.exe` file and have control over its icon, you should look into using a `.exe` generator like [JSmooth](http://jsmooth.sourceforge.net/) or [launch4j](http://launch4j.sourceforge.net/) or [JWrapper](http://www.jwrapper.com/).