C# invoke Java via C++ as a wraper.
C# invoke C++ via P/invoke. C++ starts a JVM to run the Java code.
C# code should be compiled in .NET core 2.0
You should edit the Makefile to set the Path of Java SDK export LD_LIBRARY_PATH=/usr/lib/jvm/java-1.9.0-openjdk-amd64/lib/amd64/server or add it into your enviroment
javac MyTest.java
make
dotnet build