No implementation found for long org.opencv.core.Mat.n_Mat() error Using OpenCV

Maybe you are forgetting to include the openCV library.

Include

static { 
     System.loadLibrary("opencv_java");
}

for OpenCV version 3 you should instead add:

static { 
     System.loadLibrary("opencv_java3");
}

Good Luck :)

Initialize openCV library in your activity add this code before onCreate() method

static {
    if (!OpenCVLoader.initDebug()) {
        // Handle initialization error
    }
}

add this lib in your project : https://github.com/hschott/Camdroid

I put this line on onCreate method and make sure openCvManager is installed. This worked fine for me.

OpenCVLoader.initDebug();

I have successfully eliminate the error and my app does not crash while executing this line imageMat=new Mat();

The reason for the error is that Android calls the "onCreate" method before loading the OpenCV4Android library.So i have used Async Initialization of OpenCV using OpenCVManager. I have created BaseLoaderCallback before onCreate method. And inside that i have declared new Mat() like this:

private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
    @Override
    public void onManagerConnected(int status) {
        switch (status) {
            case LoaderCallbackInterface.SUCCESS:
            {
                Log.i("OpenCV", "OpenCV loaded successfully");
                imageMat=new Mat();
            } break;
            default:
            {
                super.onManagerConnected(status);
            } break;
        }
    }
};

Then in onResume() i have checked if OpenCV library have been loaded and initialized from within current application package or not. The codes are as follows:

public void onResume()
{
    super.onResume();
    if (!OpenCVLoader.initDebug()) {
        Log.d("OpenCV", "Internal OpenCV library not found. Using OpenCV Manager for initialization");
        OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_0_0, this, mLoaderCallback);
    } else {
        Log.d("OpenCV", "OpenCV library found inside package. Using it!");
        mLoaderCallback.onManagerConnected(LoaderCallbackInterface.SUCCESS);
    }
}

And my error is gone. My full updated java class is here.

Reference links :

1. Async Initialization of OpenCV on Android using OpenCVManager
2. Tutorial1Activity.java