How to import a class from default package

I can give you this suggestion, As far as know from my C and C++ Programming experience, Once, when I had the same kinda problem, I solved it by changing the dll written structure in ".C" File by changing the name of the function which implemented the JNI native functionality. for example, If you would like to add your program in the package "com.mypackage", You change the prototype of the JNI implementing ".C" File's function/method to this one:

JNIEXPORT jint JNICALL
Java_com_mypackage_Calculations_Calculate(JNIEnv *env, jobject obj, jint contextId)
{
   //code goes here
}

JNIEXPORT jdouble JNICALL
Java_com_mypackage_Calculations_GetProgress(JNIEnv *env, jobject obj, jint contextId)
{
  //code goes here
}

Since I am new to delphi, I can not guarantee you but will say this finally, (I learned few things after googling about Delphi and JNI): Ask those people (If you are not the one) who provided the Delphi implementation of the native code to change the function names to something like this:

function Java_com_mypackage_Calculations_Calculate(PEnv: PJNIEnv; Obj: JObject; contextId: JInt):JInt; {$IFDEF WIN32} stdcall; {$ENDIF} {$IFDEF LINUX} cdecl; {$ENDIF}
var
//Any variables you might be interested in
begin
  //Some code goes here
end;



function Java_com_mypackage_Calculations_GetProgress(PEnv: PJNIEnv; Obj: JObject; contextId: JInt):JDouble; {$IFDEF WIN32} stdcall; {$ENDIF} {$IFDEF LINUX} cdecl; {$ENDIF}
var
//Any variables you might be interested in
begin
//Some code goes here
end;

But, A final advice: Although you (If you are the delphi programmer) or them will change the prototypes of these functions and recompile the dll file, once the dll file is compiled, you will not be able to change the package name of your "Java" file again & again. Because, this will again require you or them to change the prototypes of the functions in delphi with changed prefixes (e.g. JAVA_yourpackage_with_underscores_for_inner_packages_JavaFileName_MethodName)

I think this solves the problem. Thanks and regards, Harshal Malshe

From the Java language spec:

It is a compile time error to import a type from the unnamed package.

You'll have to access the class via reflection or some other indirect method.

There is a workaround for your problem. You can use reflection to achieve it.

First, create an interface for your target class Calculatons :

package mypackage;

public interface CalculationsInterface {  
    int Calculate(int contextId);  
    double GetProgress(int contextId);  

}

Next, make your target class implement that interface:

public class Calculations implements mypackage.CalculationsInterface {
    @Override
    native public int Calculate(int contextId);
    @Override
    native public double GetProgress(int contextId);
    static  {
        System.loadLibrary("Calc");
    }
}

Finally, use reflection to create an instance of Calculations class and assign it to a variable of type CalculationsInterface :

Class<?> calcClass = Class.forName("Calculations");
CalculationsInterface api = (CalculationsInterface)calcClass.newInstance();
// Use it 
double res = api.GetProgress(10);

Classes in the default package cannot be imported by classes in packages. This is why you should not use the default package.