Load and storage/save an image in OpenCV Java Mat class

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I really don't know what to do. We have to write a OpenCV program with using Java. And we have to load and storage an image in the Mat-Class from OpenCV. I never worked with OpenCV. And additional I am not really the best in programming Java. So I really don't know how to start and what to do next :(

I only think that I need to use the Highgui imread and imwrite. But dont know how to write it down :(

Pls could anybody here send me a example code with loading and storage images in Mat-Class from OpenCV using Java?

It would be such a big help for me.