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: 
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/).
I would recommend Resource Hacker to change the icon of your programs.

1. Install Resource Hacker (latest build).
2. Go to your executable file.
3. Open it with Resource Hacker (right mouseclick, and there should be an option to do that or else you could just click open with).
4. It will open and show some directories, also one called "Icon", open that one, and right click one one of the icon files (stars with some numbers after that), there will be an option: "replace icon ... Ctrl + R", click that one and replace your icon.