Exception in thread "main" java.lang.NoClassDefFoundError: org/opencv/core/Core

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Hi, I was doing a tutorial from here: "https://docs.opencv.org/3.4/d1/d0a/tu..." But the console from eclipse shows me:

i tried many things:

1.- Change from "System.loadLibrary(Core.NATIVE_LIBRARY_NAME)" to "System.loadLibrary("opencv_java2411.dll")"

2.-Change version of OpenCv, i tried 343 and 2311 version.

3.-Change from JDK 12 to JDK 8 and i get the same error.

4.-Change java version, i tried java 1.7 and got an error with reference a main function no exist.

i'm new in java, so maybe i'm lossing something important into configuration or installation, or other thing.

PD: Im just getting error with Opencv codes, i tried a simple code with only java resources and it works fine.

Please, help.