Question

For some reason i am having problems centering my panel vertically that is located inside another panel. I do exactly as the examples i studied but still no luck.

Down there is my code. Despite using setAlignmentY(0.5f) on my container panel, it still wont center when i resize the window.

Also the components inside container panel wont center either, despite setAligenmentX(0.5f).

I wonder if there is a solution for this, I pretty much tried everything out there but couldnt find a solution.

JLabel idLabel;
    JLabel passLabel;
    JTextField id;
    JTextField pass;
    JButton enter;
    JPanel container;

    public JournalLogin()
    { 
        //setLayout(new FlowLayout());
        //setPreferredSize(new Dimension(500, 500));
        //setBorder(BorderFactory.createEmptyBorder(100, 100, 100, 100));


        container = new JPanel();
        container.setLayout(new MigLayout());
        container.setAlignmentX(0.5f);
        container.setAlignmentY(0.5f);
        container.setPreferredSize(new Dimension(300, 300));
        container.setBorder(BorderFactory.createTitledBorder("Login"));
        add(container);

        idLabel = new JLabel("ID:");
        idLabel.setAlignmentX(0.5f);
        container.add(idLabel);

        id = new JTextField();
        id.setText("id");
        id.setAlignmentX(0.5f);
        id.setPreferredSize(new Dimension(80, 20));
        container.add(id, "wrap"); 

Answer 1

setAlignmentX and Y are not the way to go about doing this. One way to center a component in a container is to have the container use GridBagLayout and to add the component without using any GridBagConstraints, a so-called default addition. There are other ways as well.

For example to alter Nick Rippe’s example (1+ to him):

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridBagLayout;

import javax.swing.*;

public class UpdatePane2 extends JPanel {
   private static final int PREF_W = 300;
   private static final int PREF_H = 200;

   public UpdatePane2() {
      JPanel innerPanel = new JPanel();
      innerPanel.setLayout(new BorderLayout());
      innerPanel.add(new JLabel("Hi Mom", SwingConstants.CENTER), 
            BorderLayout.NORTH);
      innerPanel.add(new JButton("Click Me"), BorderLayout.CENTER);

      setLayout(new GridBagLayout());
      add(innerPanel);
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   private static void createAndShowGui() {
      JFrame frame = new JFrame("UpdatePane2");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(new UpdatePane2());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}