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JNI - static variables vs. instance variables

Frank Hale
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Joined: Mar 25, 2000
Posts: 230
Okay I am having a hell of a time trying to figure out why my native method can change static variables and not instance variables in a java class.
Basically I have a native method which returns a new class which holds a long value. Its how purpose in life is to hold one long variable.
The class is like this:

Now I have a method inside another class which returns a Window object with its handle;

I wanna do something like below, but it only works if I use a static variable in my Window class.

When CreateWindow is called it returns a new Window object with its handle. The problem is if I make the handle static then the handle gets passed from C to java. If I leave off the static because I would rather not have it static then the handle doesn't get passed to java from the C function.
Any help would be greatly appreciated.
Should I be so worried about using a static versus an instance variable? Does it make that much of a difference if I leave it as static?
Amit Zzz Kulkarni
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Joined: Jul 05, 2000
Posts: 30
It is definitely worse to access it as a static, why not make an object and access it as an instance ? I recall that I had faced the same problem and I made an object.
Frank Hale
Ranch Hand

Joined: Mar 25, 2000
Posts: 230
Yes I finally figured out how to access instance variables from C. I just stuff my C pointer into a Java int and then pass it back to C from Java in subsequent calls and cast it to its type. It works just like I expect it to.
I'm well on my way to a Xlib interface for Java. WooHoo!!!
If you've ever seen the Aewm window manager then I am converting it to Java using my interface, it should be pretty slick. And best of all the memory foot print has been relatively small.
It is sorta covered in the JavaRanch Style Guide.
subject: JNI - static variables vs. instance variables