Java HotSpot Virtual Machine

I am trying to implement a way of using the EnumChildWindows function using java. However I am running into some problems that I am unsure how to solve.

I have properly declared my native method in my java class like so..

 public static native boolean enumChildWindows( long parentHandle, Callback callback, long lparam );

According to MSDN, the syntax of the EnumChildWindows function in user32 is

BOOL EnumChildWindows(      
    HWND hWndParent,
    WNDENUMPROC lpEnumFunc,
    LPARAM lParam
);

..so I may seem a bit all unclear here.. but how do I declare my import in my C++ file so that it takes a jobject as one of its parameters i guess

[DllImport("user32")]
extern "C" long EnumChildWindows ( long handle, ??? callback, long lParam );

Also, how do I access it when in the body of my native method..

JNIEXPORT jboolean JNICALL Java_NativeFunctions_enumChildWindows
  (JNIEnv *, jclass, jlong handle, jobject callback, jlong lParam)

Basically, I am wanting to do the following

EnumChildWindows( handle, callback, lParam );

but I am unsure of how to go about doing that. Any help would be appreciated.