Swing is already more than capable of using a Win32 window itself:

class Main
{
       public static void main(String[] args)
       {
               JFrame frame=new JFrame();
               frame.add(new JButton("Boo");

frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
               frame.pack();
               frame.setVisible(true);
       }
}

As of Java 6, on Windows components are rendered using the native OS'
renderer (true at least for Windows and GTK, afaik), and Java has
supported native windows (as above) for years and years.

SWT provides access to native components more directly.

Your research sounds like a wheel reinvention.

If you want to paint a component to a custom graphics context, you can
do this by calling paintComponent and passing a Graphics object in, for
example, obtained from an Image.

I'm not sure, but you might want to look at the projects on dev.java.net
that deal with desktop integration. There might be stuff to get you
started or even help in you: https://javadesktop.dev.java.net/

Some years ago there was a JavaBean to ActiveX bridge, which seemed to
work fairly well back then. I have no idea whether it still exists.

Thomas