import java.awt.GridBagLayout;
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class MainGridLayoutPanel2 {

    public static void main(String[] args) {
        JFrame vindu = new JFrame("GridLayout");
        vindu.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panel = new JPanel(new GridLayout(4, 4, 5, 5));
        for (int i = 0; i < 16; i++) {
            JPanel buttonPanel = new JPanel(new GridBagLayout());
            buttonPanel.add(new JButton(String.valueOf(i)));
            panel.add(buttonPanel);
        }

        vindu.add(panel);
        vindu.setSize(500, 500);
        vindu.setVisible(true);
    }
}