为什么在运行 GUI 时 JLabel 或 JButton 不显示？

Question

I have been playing around with numerous solutions but none of them seems to work. in the constructor, there is a default initComponents() which I can not change. So I created a second method called myComponents() . The class I am using extends JFrame so I do not need to create another frame in any initializer. I created a JPanel with a vertical Boxlayout , 2 labels, 1 text field, and 1 button. I added the panel to the frame then I added all the components to the panel then packed everything.

I am unsure as to why nothing shows up besides the frame when it is run.

import javax.swing.BoxLayout;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

/**
 *
 * @author gpbli
 */
public class MAINFRAME extends javax.swing.JFrame {

    /**
     * Creates new form MAINFRAME
     */
    //MAINFRAME frame = new MAINFRAME();
    JPanel homescreen = new JPanel();

    JLabel numOfIngredLabel = new JLabel();
    JTextField numOfIngred = new JTextField();
    JButton okButton = new JButton();
    JLabel logo = new JLabel();

    ImageIcon img = new ImageIcon("logo_resized.png");
    public MAINFRAME() {
        initComponents();
        myComponents();
    }
    public void myComponents(){
        BoxLayout box = new BoxLayout(homescreen,BoxLayout.Y_AXIS);
        homescreen.setLayout(box);
    
    numOfIngredLabel.setText("How many Ingredients");
    numOfIngred.setText("");
    okButton.setText("OK");
    logo.setText(" ");
    logo.setIcon(img);
    
    add(homescreen);
    homescreen.add(logo);
    homescreen.add(numOfIngredLabel);
    homescreen.add(numOfIngred);
    homescreen.add(okButton);
    
    numOfIngredLabel.setVisible(true);
    numOfIngred.setVisible(true);
    okButton.setVisible(true);
    logo.setVisible(true);
    
    pack();
    revalidate();
    
    
}
/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 400, Short.MAX_VALUE)
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 300, Short.MAX_VALUE)
    );

    pack();
}// </editor-fold>                        

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {
    /* Set the Nimbus look and feel */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */
    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(MAINFRAME.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(MAINFRAME.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(MAINFRAME.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(MAINFRAME.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    
    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new MAINFRAME().setVisible(true);
        }
    });
}

// Variables declaration - do not modify                     
// End of variables declaration                   
}

Answer 1

The appearance of initComponents() suggests the IDE is expecting the programmer to use the GUI builder, while the myComponents() is the programmer taking control of the GUI construction to code it by hand.

Use one or the other. I'd always use the latter, which does not require the JFrame to be extended. In fact, creating the main view of the GUI in a JPanel and adding that single component to a JFrame is the way we would typically recommend.

Note: See also the accepted answer to: Netbeans GUI editor generating its own incomprehensible code