Mam problem z centrowaniem JTexfielda w moim programie. Pole tekstowe nie jest wyrównane z przyciskiem JButton. Próbowałem wcześniej za pomocą x.setHoriontalAlignment (JTextfield.CENTER); ale bez skutku. Jakieś pomysły?

import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JPanel;
import java.awt.Container;
import java.awt.GridLayout;
import java.awt.GridBagLayout;

public class WidgetProject implements ActionListener
{
 //class constants
private static final Color BUTTON_COLOUR1 = Color.WHITE;
private static final int BUTTON_HEIGHT = 75;
private static final int BUTTON_WIDTH = 400;
private static final int TEXTFIELD_HEIGHT = 400;
private static final int TEXTFIELD_WIDTH = 50;
private static final String SECONDS_PER_MINUTE = "Seconds to Minutes or Minutes to Seconds";
private static final String BUTTON2_MODIFIED_LABEL = "yes";
private static final String POUNDS_PER_KILOGRAM = "Pounds to Kilograms or Kilograms to Pounds";
private static final String CHANGE_MY_LABEL = "1";
private static final int HEIGHT = 400;
private static final int WIDTH = 400;

// instance fields
 private JButton button1;
private JButton button2;
private JButton button3;
private JButton button4;
private JFrame frame;
private JTextField textInput;
private JPanel panel;

/**
 * A free-standing frame with two buttons.
 * 
 * @param title the title of this frame
 */
public WidgetProject(String title)
{
    // Establish the frame.
    frame = new JFrame(title);
    frame.setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.Y_AXIS));
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setPreferredSize(new Dimension(WIDTH, HEIGHT));

    // Establish button dimensions.
    Dimension buttonDimension = new Dimension(BUTTON_WIDTH, BUTTON_HEIGHT);

    // Establish Textfield dimensions.
    Dimension textDimension = new Dimension(TEXTFIELD_HEIGHT, TEXTFIELD_WIDTH);

    // Create and add the first button.
    button1 = new JButton(SECONDS_PER_MINUTE);
    button1.setActionCommand(CHANGE_MY_LABEL);
    button1.addActionListener(this);
    button1.setPreferredSize(buttonDimension);
    button1.setMinimumSize(buttonDimension);
    button1.setMaximumSize(buttonDimension);
    button1.setBackground(BUTTON_COLOUR1);
    frame.add(button1);

     // Create and add the second button.
    button2 = new JButton(POUNDS_PER_KILOGRAM);
    button2.setActionCommand(CHANGE_MY_LABEL);
    button2.addActionListener(this);
    button2.setPreferredSize(buttonDimension);
    button2.setMinimumSize(buttonDimension);
    button2.setMaximumSize(buttonDimension);
    button2.setBackground(BUTTON_COLOUR1);
    frame.add(button2);

    // Create an input text field.
    textInput = new JTextField(20);
    textInput.setPreferredSize(textDimension);
    textInput.setMinimumSize(textDimension);
    textInput.setMaximumSize(textDimension);
    textInput.setHorizontalAlignment(JTextField.CENTER);
    panel = new JPanel();
    panel.add(textInput);
    String string = textInput.getText();


    // Display the frame and text field.
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
    frame.add(textInput);

} // koniec konstruktora ButtonDuo