How to interact with native code from Java

1. JNI – Java Native Interface
How to persuade my Java application to talk
to evil evil C native code

2. • WHAT?
• WHY?
• WHY NOT?
• THE ACTUAL CODE
• GOODIES

3. Er… WHAT?
Java applications
Native applications

4. But, but…
WHY?

5. But, but…
WHY?
Allows native API function calls

6. But, but…
WHY?
Usage of existing native libraries

7. But, but…
WHY?
Execution of time-critical code

8. OK, so
WHY NOT?
Use of JNI should be avoided
whenever reasonably possible!

9. Example
Java native function declaration first:

10. Example

11. Example

12. Example

13. Example

14. Example

15. Example
Careful!

16. Example

17. Example

18. Example

19. Exceptions?!
Doable but annoying.

20. Other things to know
• Forget about garbage collection
• Java JVM is nazi about its memory space

21. I DON’T EXIST
jernej@virag.si
Skype: izacus