Jar launcher excruciatingly slow

I'm currently working on an independent project for school, where I make a visualizer for the Mandelbrot set. I have a basic version of the program, and wanted to package it into a jar and test it on other systems. When I tested on my mac, I noticed that launching from terminal worked normally (just like from intellij or code)

java -jar Mandy.jar

However, double clicking the executable executes the same program at a snail's pace. From what I can tell, over 100x slower per paint cycle (I will post a time profile soon)

I've looked all over, and have been unable to find an explanation for this. I assume it has to do with macos's jar launcher, but there was very little information available on it.

Does anyone have any idea what could cause this? Thanks in advance.

Here is the code and executable jar in case someone wanted to see for themselves: repo

Edit: This is being experienced on a macos system with (only) jdk 11 on it. All other JRE's and JDK's have been uninstalled.

It is noteworthy that when compiled and executed with java 8, the same slowness was experienced regardless of launch method.

Most likely you have more than one JDK or JRE installed on the system, and running java -jar on the command line uses a different java executable than double clicking a jar from the finder.

Right click on the jar in the finder for other open options, or use 'get info', then check out what executable is being used to run it. I bet it will not match with what which java prints on the command line. Find a way to uninstall that JVM, or change the app to be used to run jar files and then click the 'for all such files' option in the get info widget.