public class A extends B{

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

protected static void A(){
    //- Frame
    JFrame frame_loading = new JFrame("Loading");
    frame_loading.setSize(250, 100);
    frame_loading.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame_loading.setLayout(new BorderLayout());
    frame_loading.setLocationRelativeTo(null);      // Center in screen

    //- Text
    JLabel label_loading = new JLabel("        Loading... ");
    label_loading.setFont(new Font("Tahoma", 0, 15));
    frame_loading.add(label_loading, BorderLayout.WEST);

    //- Text
    JLabel label_number = new JLabel();
    label_number.setFont(new Font("Tahoma", 0, 15));
    frame_loading.add(label_number, BorderLayout.CENTER);

    frame_loading.setVisible(true);

    for(...){
        label_number.setText(Integer.toString(i + 1));
    }

frame_loading.dispose();
}

JPanel panel = new JPanel();
panel.setLayout(new BorderLayout());

//- ContentPane
Container pane = frame_loading.getContentPane();
pane.setLayout(new BorderLayout());

frame_loading.add(panel);
frame_loading.pack();