在 JFrame 上居中 JLabel

Question

I've been reading around lately on centering a JLabel in a JPanel. I've seen a lot of the following two answers:

label.setHorizontalAlignment(JLabel.CENTER);

and in the creation of the JLabel

static JLabel label = new JLabel("Some Text Here", SwingConstants.CENTER);

Neither of these options that I have tried have worked. All the text becomes left alligned with both of these answers (I've even tried using both of them at the same time, and no luck). Here is the full code for one of my labels with its instantiation and everything:

//JLabel title = new JLabel("Title", SwingConstants.CENTER);
JLabel title = new JLabel("Title");
title.setVisible(true);
title.setForeground(Color.BLACK);
title.setFont(new Font("Monospaced", Font.BOLD, 32));
//title.setHorizontalAlignment(JLabel.CENTER);
title.setLocation((int)width/2-190,10);
title.setSize(250,100);
frame.add(title);

I commented out the code that just left aligns it and is supposed to work. For the set location, I'm using:

static Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
static double width = screenSize.getWidth();
static double height = screenSize.getHeight();

to define the screen's parameters, and then use that to keep the centering somewhat abstract. However, obviously monitor size changes and 9 times out of 10, the code I have here for setLocation isn't going to center it on your screen.

I'm really curious to why this isn't working for me. Is it because I'm not adding the JLabel to a JPanel? I was under the assumption that JLabel could lay over a JFrame in the same way it layed over a JPanel.

EDIT

I just also tried

frame.add(title,BorderLayout.CENTER);

and had the same result as the other 2 options above.

Answer 1

This works for me (NOTE: SwingConstants.CENTER, not SwingConstraints.CENTER):

   public static void main( String[] args ) {
      SwingUtilities.invokeLater( new Runnable() {
         @Override
         public void run() {
            JFrame jf = new JFrame();
            jf.addWindowListener( new WindowAdapter() {
               @Override
               public void windowClosing( WindowEvent arg0 ) {
                  System.exit( 0 );
               }
            } );
            JLabel t = new JLabel( "Centered", SwingConstants.CENTER );
            jf.add( t, BorderLayout.CENTER );
            jf.setSize( 300, 300 );
            jf.setVisible( true );
         }
      } );
   }

Answer 2

Also:

import java.awt.Color;
import java.awt.GridBagLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.border.LineBorder;

public class CenterDemo2 {
  public static void main(final String[] args ) {
      SwingUtilities.invokeLater( new Runnable() {
         @Override
         public void run() {
            final JFrame frame = new JFrame("Test frame");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

            final JLabel label = new JLabel("Test label");
            label.setBorder(new LineBorder(Color.BLUE, 2)); //Adding a border for clarity.

            //Most significant two lines of code:
            final JPanel containerPanel = new JPanel(new GridBagLayout());
            containerPanel.add(label);

            frame.getContentPane().add(containerPanel); //or: frame.setContentPane(containerPanel);
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
         }
      });
   }
}  

The JLabel is in the (horizontal and vertical) center of the JPanel .

Screenshot, after dragging with the mouse to resize the frame: