Patience is a vitue. After letting the problem of Java on my Synology NAS 509+ rest (see Yet another Try to get Java running and Compiling for Synology DS509+) the problem solved itself.
After upgrading to the DiskManager 3.0 and all installed packages I did a routinely check on the IPKG repository and discovered the package JamVm which can be used as a java runtime. Then I saw that the new disk manager brought the jikes installation which can be used to compile java classes.
Jikes works as expected:
echo "public class App{
public static void main(String[] args){
System.out.println("Hello World");
}
}" > App.java
jikes -cp /opt/lib/rt.jar App.java
However jamvm throws a Segmentation fault (core dumped) error when invoked.
jamvm -cp /opt/lib/rt.jar App
Unfortunately it is so that jamvm is only available for ARM based processors and not PowerPC.