import java.awt.*;
import java.io.*;
import javax.imageio.ImageIO;
import javax.swing.*;

public class ResourceTest extends JFrame {

    public ResourceTest() { SwingUtilities.invokeLater(this::UI); }

    private void UI() {

        InputStream is = getClass().getResourceAsStream("icon.jpg");
        ImageIcon icon;
        try { icon = new ImageIcon(ImageIO.read(is)); }
        catch (IOException e) { throw new RuntimeException(e); }

        Image img = Toolkit.getDefaultToolkit().getImage(
            new File("icon.jpg").getAbsolutePath());

        getContentPane().setLayout(new GridLayout(1, 2));
        setSize(200, 100);

        JButton b1 = new JButton();
        b1.setIcon(icon);
        add(b1);

        JButton b2 = new JButton();
        b2.setIcon(new ImageIcon(img));
        add(b2);

        setLocation(100, 100);
        setResizable(false);
        setUndecorated(true);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }

    public static void main(String[] args) { new ResourceTest(); }
}