It's not neccessary that a Visual Basic DLL is going to be a COM object. If the Visual basic DLL is a COM object, then you can use JACOB or other Java-COM bridges to call the DLL. If it's not, then you will have to develop your own C++ JNI layer that will wrap the Visual basic DLL and export the functions to Java
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a bit of art, as a gift, the permaculture playing cards