Javah problem - super class could not be found !!

Question

Hi all,
i have already posted this message but i didn't get enough help to solve my poor situation.
and this is my problem:
i got in my project (myProject) MyClass class.
i wrote in another java class ,in OtherClass.class ,jni function that use MyClass object as parameter to the jni interface, as follow:
private native int myFunction (MyClass obj); //function in OtherClass
when i write the javah command line :
javah -jni OtherClass (in order to create OtherClass.h)
i always get the following error:
A required super class myPackage.MyClass could not be found.
my qoustion is how can i let the javah command line to know about the existence of myPackage.MyClass and how can i create and .h file when i using other class instance as jni function parameter in other class??
Thanks Sendy.

Answer 1

Lets define a few terms here.
Java can be a java virtual machine which is what runs when you type 'java' on the command line. It is also represented by the compiler which runs when you type 'javac'. And in your case it also is represented by 'javah'.
The class path defines where java finds classes that it needs.
In older versions of java you had to tell it where to find everything. It couldn't even find java.lang.String unless you told it were it was. Now days you have to tell it where to find stuff that you add (or where 3rd party libraries are.)
There are two ways to define the class path: a command line option and an environment variable.
A class path can, currently, have three types of things in it:
-A path to a zip file
-A path to a jar file
-A path
For example
-Path to zip file in windows: C:\mystuff\mylib\mystuff.zip
-Path to zip file in unix: /opt/system/projects/mystuff/mystuff.zip
-Path to jar file in windows: C:\mystuff\mylib\myjar.jar
-Path to jar file in unix: /opt/system/projects/mystuff/myjar.jar
-Path in windows: C:\mystuff\mylib
-Path in unix: /opt/system/projects/mystuff
Zip files aren't used as much anymore, but you should at least be aware of them.
Java uses the class path to look for classes which are stored in files. It does this by translating the class name into a file name. It uses packages as directory names and class names as file names. So in your case it would try to find a class called myPackage.MyClass in a file called myPackage\MyClass.class. It would try to find that in any zip files, jar files, in in any paths that you specified in the class path.
So java is trying to find myPackage\MyClass.class in your class path. It would try to find that in any zip files, jar files, in in any paths that you specified in the class path.
Right now your class path is probably just "." which means that if you do the following commands
cd C:\mystuff
javah -jni OtherClass
Then java is going to try to find myPackage.MyClass in the following file
.\myPackage\MyClass.class
That, because you 'cd' to C:\mystuff, translates to the following absolute path
C:\mystuff\myPackage\MyClass.class
So if java doesn't find that file then it is going to tell you that it can't find the file.
So where is your file? Let's say it is here.
C:\work\lib\myPackage\MyClass.class
So you must tell javah where the root is. Keep in mind that 'myPackage' must be part of the path. That is not optional. The root is the directory above 'myPackage'. So the root is
C:\work\lib
So now you have a path that is ready for your class path. So your javah command could look like this
javah -classpath ".;C:\work\lib" -jni OtherClass
Or using an environment variable
set CLASSPATH=.;C:\work\lib
javah -jni OtherClass
Keep in mind in the above that class path is a generic term and there can be other ways to define it. For example the Sun command "java" allows you to use "-classpath" or "-cp".
So does the above help?