codice:
import java.awt.*;
import javax.swing.*;

public class ImgGridBag extends JFrame {

   public ImgGridBag() {
      Container c = getContentPane();
      c.setLayout( new BorderLayout() );

      c.add(getPannelloPrincipale(), BorderLayout.CENTER);

      setTitle("Titolo");
      setSize(800, 600);
      setDefaultCloseOperation( EXIT_ON_CLOSE );
      setLocationRelativeTo( null );
      setVisible( true );
   }

   private Component getPannelloPrincipale() {
      JPanel jp = new JPanel();
      GridBagLayout layout = new GridBagLayout();
      GridBagConstraints constraints = new GridBagConstraints();
      jp.setLayout( layout );

      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 0;
      constraints.gridy = 0;
      constraints.gridwidth = 1;
      constraints.gridheight = 1;

      JLabel lbl = new JLabel( new ImageIcon("immagine.png") );
      layout.setConstraints(lbl, constraints);

      jp.add( lbl );

      return jp;
   }

   public static void main(String[] args) {
      ImgGridBag igb = new ImgGridBag();
   }
}
Esempio funzionante.


Ciao.