installing netbeans did not help, still have error:
checking for javac... javac -Xlint:unchecked,cast,divzero,empty,finally,overrides
checking if javac -Xlint:unchecked,cast,divzero,empty,finally,overrides is a version of gcj... no
checking if javac -Xlint:unchecked,cast,divzero,empty,finally,overrides works... configure: error: The Java compiler javac -Xlint:unchecked,cast,divzero,empty,finally,overrides failed (see config.log, check the CLASSPATH?)
make[3]: *** [Makefile:93: /home/boris/rutos/rutos-ath79-rut9-gpl/build_dir/target-mips_24kc_musl/classpath-0.99/.configured_68b329da9893e34099c7d8ad5cb9c940] Error 1
make[3]: Leaving directory '/home/boris/rutos/rutos-ath79-rut9-gpl/package/libs/classpath'
time: package/libs/classpath/compile#15.61#3.62#18.70
ERROR: package/libs/classpath failed to build.
make[2]: *** [package/Makefile:114: package/libs/classpath/compile] Error 1
make[2]: Leaving directory '/home/boris/rutos/rutos-ath79-rut9-gpl'
make[1]: *** [package/Makefile:108: /home/boris/rutos/rutos-ath79-rut9-gpl/staging_dir/target-mips_24kc_musl/stamp/.package_compile] Error 2
make[1]: Leaving directory '/home/boris/rutos/rutos-ath79-rut9-gpl'
make: *** [/home/boris/rutos/rutos-ath79-rut9-gpl/include/toplevel.mk:234: world] Error 2