I would use SomeClass.class.getResourceAsStream("...")
as in the following example:
public static void main(String[] arguments) throws IOException {
JFrame frame1 = new JFrame();
frame1.setTitle("Frame1");
frame1.setSize(500, 500);
frame1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
FlowLayout flo = new FlowLayout();
frame1.setLayout(flo);
InputStream resourceAsStream = IconTest.class.getResourceAsStream("strawberry.jpg");
Image image = ImageIO.read(resourceAsStream);
JLabel label1 = new JLabel(new ImageIcon(image));
frame1.add(label1);
frame1.setVisible(true);
}