Here are a few session snippets showing the two JNI examples...

shell/iX> java -version
java version "JDK 1.1.7B"

shell/iX> uname -a
MPE/iX TELESTO  C.55.00 C.05.08  SERIES 987SX

shell/iX> ls -l
-rwxr-----   1 USER.IX           IX           823 Aug 14 09:54 AskOp.java
-rwxr-----   1 USER.IX           IX           716 Aug 14 11:43 Makefile
-rwxr-----   1 USER.IX           IX           336 Aug 14 11:36 v1c89.c
-rwxr-----   1 USER.IX           IX           894 Aug 14 11:49 v1gcc.c
-rwxr-----   1 USER.IX           IX          1077 Aug 14 10:41 v2cob.s
-rwxr-----   1 USER.IX           IX          1201 Aug 14 11:52 v2gcc.c

shell/iX> javac AskOp.java

shell/iX> javah -jni AskOp

shell/iX> make gcc-c89
 (...) 

shell/iX> ls -l
-rw-rw----   1 USER.IX           IX           945 Aug 14 12:00 AskOp.class
-rw-rw----   1 USER.IX           IX           571 Aug 14 10:09 AskOp.h
-rwxr-----   1 USER.IX           IX           823 Aug 14 09:54 AskOp.java
-rwxr-----   1 USER.IX           IX           716 Aug 14 11:43 Makefile
-rwxrwx---   1 USER.IX           IX         30976 Aug 14 12:01 libXY.sl
-rwxr-----   1 USER.IX           IX           336 Aug 14 11:36 v1c89.c
-rw-rw----   1 USER.IX           IX          1024 Aug 14 12:01 v1c89.o
-rwxr-----   1 USER.IX           IX           894 Aug 14 11:49 v1gcc.c
-rw-rw----   1 USER.IX           IX          1461 Aug 14 12:01 v1gcc.o
-rwxr-----   1 USER.IX           IX          1077 Aug 14 10:41 v2cob.s
-rwxr-----   1 USER.IX           IX          1201 Aug 14 11:52 v2gcc.c

shell/iX> export LD_LIBRARY_PATH=$PWD

shell/iX> java AskOp
testing printOp
testing printOpReply
operator replied ok1

   | Here is the console output from the above test:
   |
   | 14:01/#S2/73/Hello Operator, testing Java Native Interface
   | ?14:01/#S2/73/Could you please reply OK? (MAX CHARS.=31)?
   |
   | :reply 73, ok1

shell/iX> make clean
rm -f *.o libXY.sl

shell/iX> make gcc-cob
 (...)
 
shell/iX> java AskOp
testing printOp
testing printOpReply
operator replied ok2

   | Here is the console output from the above test:
   |
   | 14:02/#S2/69/Hello Operator, testing Java Native Interface
   | ?14:02/#S2/69/Could you please reply OK? (MAX CHARS.=31)?
   |
   | :reply 69,ok2

shell/iX> make clean
rm -f *.o libXY.sl

Pure gcc or pure c89 (native part) implementations are also possible.