Java Native Access (JNA) is a popular Java library that allows you to call native code from Java programs. It simplifies the process of interacting with native libraries and provides a seamless way to pass and receive array data between Java and native code.

In this blog post, we will explore how to pass and receive arrays in Java JNA using the NativeLibrary and Structure classes.

Passing Arrays as Parameters

To pass arrays as parameters to native functions, we can use the Structure class provided by JNA. The Structure class allows us to define the structure and layout of the native data to be passed. Here’s an example:

import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.Structure;

// Native library interface
public interface MyNativeLibrary extends Library {
    MyNativeLibrary INSTANCE = Native.loadLibrary("myNativeLibrary", MyNativeLibrary.class);

    void processIntArray(int[] array, int size);
}

public class Main {
    public static void main(String[] args) {
        int[] array = {1, 2, 3, 4, 5};

        MyNativeLibrary.INSTANCE.processIntArray(array, array.length);
    }
}

In the above code, we define a native library interface MyNativeLibrary that extends the Library class provided by JNA. We declare a processIntArray function that takes an int array and its size as parameters.

Inside the main method, we create an int array array and pass it to the processIntArray function along with the array size. The JNA library handles the conversion and passes the array to the native code.

Receiving Arrays as Return Values

To receive arrays as return values from native functions, we can use the Structure.toArray() method provided by JNA. This method converts a Structure object into a Java array. Here’s an example:

import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.Structure;

// Native library interface
public interface MyNativeLibrary extends Library {
    MyNativeLibrary INSTANCE = Native.loadLibrary("myNativeLibrary", MyNativeLibrary.class);

    int[] getIntArray();
}

public class Main {
    public static void main(String[] args) {
        MyNativeLibrary myLibrary = MyNativeLibrary.INSTANCE;

        int[] array = myLibrary.getIntArray();
        
        // Access and print elements of the array
        for (int i = 0; i < array.length; i++) {
            System.out.println(array[i]);
        }
    }
}

In the above code, we define a native library interface MyNativeLibrary with a method getIntArray that returns an int array.

Inside the main method, we call getIntArray on the MyNativeLibrary instance myLibrary and assign the returned array to the array variable. We can then access and process the elements of the array as usual.

JNA takes care of converting the array returned from the native code into a Java array using the Structure.toArray() method.

Conclusion

Passing and receiving arrays in Java JNA is made straightforward with the help of the Structure class and its associated methods. By following the examples provided in this blog post, you can easily integrate native code that works with arrays into your Java applications.

#Java #JNA #NativeAccess #Arrays