Classe: CenteredPanelExample - fig1

 1 package centeredpanelexample;
 2 
 3 import javax.swing.*;
 4 import java.awt.*;
 5 import java.awt.event.ComponentAdapter;
 6 import java.awt.event.ComponentEvent;
 7 
 8 public class CenteredPanelExample {
 9     public static void main(String[] args) {
10         SwingUtilities.invokeLater(() -> {
11             JFrame frame = new JFrame("Esempio JPanel Centrato");
12             frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
13             frame.setSize(400, 300);
14             frame.setLocationRelativeTo(null); // Centra la finestra sullo schermo
15             frame.getContentPane().setLayout(null);
16             // Crea un JPanel con sfondo rosso
17             JPanel panel = new JPanel();
18             panel.setBackground(Color.RED);
19             //panel.setPreferredSize(new Dimension(100, 50));
20             panel.setBounds(50, 50, 100, 100);
21             // Aggiungi il pannello alla finestra
22             frame.add(panel);
23 
24             // Aggiungi un listener per ricollocare il pannello al centro quando 
               //  la finestra viene ridimensionata
25             frame.addComponentListener(new ComponentAdapter() {
26                 @Override
27                 public void componentResized(ComponentEvent e) {
28                     centerPanel(frame, panel);
29                 }
30             });
31 
32             // Mostra la finestra
33             frame.setVisible(true);
34         });
35     }
36 
37     // Centra il pannello all'interno della finestra
38     private static void centerPanel(JFrame frame, JPanel panel) {
39         int frameWidth = frame.getWidth();
40         int frameHeight = frame.getHeight();
41         int panelWidth = panel.getWidth();
42         int panelHeight = panel.getHeight();
43 
44         int x = (frameWidth - panelWidth) / 2;
45         int y = (frameHeight - panelHeight) / 2;
46 
47         panel.setLocation(x, y);
48     }
49 }     

Classe: CenteredPanelExample - fig2

 1 package centeredpanelexample;
 2 
 3 import javax.swing.*;
 4 import java.awt.*;
 5 
 6 public class CenteredPanelExample {
 7     public static void main(String[] args) {
 8         SwingUtilities.invokeLater(() -> {
 9             JFrame frame = new JFrame("Esempio JPanel Centrato");
10             frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
11             frame.setSize(400, 300);
12 
13             // Crea un JPanel con sfondo rosso
14             JPanel panel = new JPanel();
15             panel.setBackground(Color.RED);
16             panel.setPreferredSize(new Dimension(100, 50));
17 
18             // Imposta il layout del frame su GridBagLayout
19             frame.setLayout(new GridBagLayout());
20 
21             // Imposta le impostazioni per centrare il pannello
22             GridBagConstraints constraints = new GridBagConstraints();
23             constraints.gridx = 0;
24             constraints.gridy = 0;
25             constraints.weightx = 1.0;
26             constraints.weighty = 1.0;
27             constraints.fill = GridBagConstraints.CENTER;
28             frame.add(panel, constraints);
29 
30             // Mostra la finestra
31             frame.setVisible(true);
32         });
33     }
34 }
35      

Classe: CenteredPanelExample - fig3

1 package centeredpanelexample;
 2 
 3 import javax.swing.*;
 4 import java.awt.*;
 5 
 6 public class CenteredPanelExample {
 7     public static void main(String[] args) {
 8         SwingUtilities.invokeLater(() -> {
 9             JFrame frame = new JFrame("Esempio JPanel Centrato");
10             frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
11             frame.setSize(400, 300);
12 
13             // Crea un JPanel con sfondo rosso
14             JPanel panel = new JPanel();
15             panel.setBackground(Color.RED);
16             panel.setPreferredSize(new Dimension(100, 50));
17 
18             // Imposta il layout del frame su GridBagLayout
19             frame.setLayout(new GridBagLayout());
20 
21             // Imposta le impostazioni per centrare il pannello
22             GridBagConstraints constraints = new GridBagConstraints();
23             constraints.gridx = 0;
24             constraints.gridy = 0;
25             constraints.weightx = 1.0;
26             constraints.weighty = 1.0;
27             // Espandi sia orizzontalmente che verticalmente
28             constraints.fill = GridBagConstraints.BOTH; 
29             frame.add(panel, constraints);
30 
31             // Mostra la finestra
32             frame.setVisible(true);
33         });
34     }
35 }