Update Java Version

[cdennison]

Got this error using Java 14 so updating docs to Java 15 which worked for me.

Exception in thread "main" java.lang.UnsupportedClassVersionError: me/drton/jmavsim/Simulator has been compiled by a more recent version of the Java Runtime (class file version 59.0), this version of the Java Runtime only recognizes class file versions up to 58.0

Looks like this needs updating in the following areas - I'm happy to update the PR but I cannot test all those envs.

[hamishwillee]

Thanks @cdennison.

I've tidied up your suggested "things that need to be fixed".

• Most of these are translated copies (they automatically get fixed based on the English versions).
• The versions for other platforms (ie Linux and Windows) work with the versions of Java you get by default on those platforms. Unless that has changed (I will test) we don't want to change globally.

I'll do some testing.

[hamishwillee]

@julianoes Do you use MacOS and can you test this?

As a test point Ubuntu 20.04 uses Java 14. I just tested against latest PX4 in my VM. It works, though I do get some (different) warnings:

BUILD SUCCESSFUL
Total time: 1 second
Options parsed, starting Sim.
Starting GUI...
Feb 16, 2021 4:30:14 PM java.util.prefs.FileSystemPreferences$1 run
INFO: Created user preferences directory.
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by javax.media.j3d.JoglPipeline (rsrc:j3dcore.jar) to method sun.awt.AppContext.getAppContext()
WARNING: Please consider reporting this to the maintainers of javax.media.j3d.JoglPipeline
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
INFO  [simulator] Simulator connected on TCP port 4560.
Init MAVLink
INFO  [commander] LED: open /dev/led0 failed (22)
``

[julianoes]

@hamishwillee https://docs.px4.io/master/en/simulation/jmavsim.html#an-illegal-reflective-access-operation-has-occured

[julianoes]

As @hamishwillee says, whatever comes with Ubuntu 20.04 (which is what we're trying to support) should be fine.

[julianoes]

This is fine.

[julianoes]

@cdennison have you tried rebuilding it properly after doing rm -rf Tools/jMAVSim/out ?

[hamishwillee]

My take is that we don't change the docs because this should work for either Java and there is no point doing so unless we understand the cause of the actual problem. Any more debugging we might do @julianoes ?

[mrpollo]

fixed by #1095