on Kali 2020.2 I have added your jar file into /usr/bin (where nmap is as well), then I started your .jar file
Screenshot_2020年06月21日_20-00-23
but your file said; nmap is not runnng (prog is in the same directory). What is the issue?

openjdk version "11.0.7-ea" 2020年04月14日
OpenJDK Runtime Environment (build 11.0.7-ea+9-post-Debian-1)
OpenJDK 64-Bit Server VM (build 11.0.7-ea+9-post-Debian-1, mixed mode, sharing)

Nmap 7.80