When an instance of JLayer is created with help of JLayer(Component) constructor,
it doesn't have a ui delegate by default and so cannot be painted on screen.

import javax.swing.*;

public class LayerTest {

    private static void createGui() {
        final JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // JButton is not painted
        frame.add(new JLayer(new JButton("Hello")));

        frame.setSize(200, 200);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeAndWait(new Runnable() {
            public void run() {
                LayerTest.createGui();
            }
        });
    }
}