Double-clicking the .jar got me nowhere. "Failed to start." Note that apple doesn't use the JAVA_HOME environment variable, but has a java_home executable instead. I used the command line and my error was a little different from above.
% /usr/libexec/java_home -v ll
/Library/Java/JavaVirtualMachines/jdk-15.0.1.jdk/Contents/Home
% which java
/usr/bin/java
% /usr/bin/java --version
java 15.0.1 2020-10-20
Java(TM) SE Runtime Environment (build 15.0.1+9-1
Java HotSpot(TM) 64-Bit Server VM (build 15.0.1+9-18, mixed mode, sharing)
% echo $JAVA_HOME
% pwd
/Users/xxxxxxxxxx/RChess
% /usr/bin/java -Xmx2000m -jar ./rchess.jar
##### Heap utilization at start #####
Used Memory: 1
Free Memory: 12
Total Memory: 14
Max Memory: 2000
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.codehaus.groovy.vmplugin.v9.Java9 (file:/Users/xxxxxxxxxx/RChess/rchess_lib/groovy-3.0.6-indy.jar) to constructor com.apple.laf.AquaLookAndFeel()
WARNING: Please consider reporting this to the maintainers of org.codehaus.groovy.vmplugin.v9.Java9
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Setup Hash: 1
And RChess starts okay, I will have to do some extensive testing to see if anything is not working.
N.B. I used the Version 2.00 Linux, Mac link
http://www.rchess.de/rchess/download?version=163
But the reported version is different:
File ! About RChess -.> Version: 1.05
OK
Good work to start!
HOWEVER, if the terminal pwd is NOT the RChess directory, e.g.
% pwd
/Users/xxxxxxxxxx
% /usr/bin/java -Xmx2000m -jar ~/RChess/rchess.jar
then I get MANY more errors. The one that is under your control is:
java.io.FileNotFoundException: pieces/Standard/King-W.svg (No such file or directory)
I can start a new game, and move the pieces, but I am playing blindfold chess, the pieces don't appear on the chessboard, there is no wood background in the frame, etc. So I think you need to adjust your code to figure out where rchess.jar lives and then use that directory internally. Either that or provide an RCHESS_DIR environment variable I can set on the command line. It needs to be
$RCHESS_DIR/pieces/Standard/King-W.svg