jni calling function not work in first step

Question

hello

I have program that use JNI I use Runtime.getRuntime().exec(file path and name); for open an program and when is opened I try to set perant of this program on button listener. I have 2 Native methods that 1 long fw("titlewindow") for get handle with title of window and an other

long setparent(fw(),handle of main progarm[I'm sure is correct]);

use for set parent and both work in c++ good and in java in first event fire open program

BUT

fw function not found handle of that (return 0 in this function I use FindWindow win32 API and return export of this) and in two event fire that give handle of program good and of course open an other instance of program.

thank for any help