如何从其他方法访问JLabel？

Question

I'm working on a GUI application and what i want my code to do is that after clicking the sole button that you can perceive in my swing-based GUI, the 2 jLabels present within it make the String "Working" perceivable to the user. Here's my code:

public class DiligentGUI extends javax.swing.JFrame {

public DiligentGUI() {
    initComponents();
}
void a()
{
  fahrenheitLabel.setText("Working");  
}

@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    tempTextField = new javax.swing.JTextField();
    celsiusLabel = new javax.swing.JLabel();
    convertButton = new javax.swing.JButton();
    fahrenheitLabel = new javax.swing.JLabel();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    setTitle("Celsius Converter");

    tempTextField.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            tempTextFieldActionPerformed(evt);
        }
    });

    celsiusLabel.setText("Celsius");

    convertButton.setText("Convert");
    convertButton.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            convertButtonActionPerformed(evt);
        }
    });

    fahrenheitLabel.setText("Fahrenheit");

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()

.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                    .addComponent(tempTextField,  
javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE,  
javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addGap(12, 12, 12)
                    .addComponent(celsiusLabel))
                .addGroup(layout.createSequentialGroup()
                    .addComponent(convertButton)


.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                    .addComponent(fahrenheitLabel)))
            .addContainerGap(59, Short.MAX_VALUE))
    );

    layout.linkSize(javax.swing.SwingConstants.HORIZONTAL, new java.awt.Component[] {convertButton, tempTextField});

    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(tempTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(celsiusLabel))
            .addGap(18, 18, 18)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(convertButton)
                .addComponent(fahrenheitLabel))
            .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
    );

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

private void tempTextFieldActionPerformed(java.awt.event.ActionEvent evt) {                                              
    // TODO add your handling code here:
}                                             

private void convertButtonActionPerformed(java.awt.event.ActionEvent evt) {                                              

DiligentGUI b = new DiligentGUI();
b.a();
celsiusLabel.setText("Working");
}                                             

/**
 * @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(DiligentGUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(DiligentGUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(DiligentGUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(DiligentGUI.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 DiligentGUI().setVisible(true);
        }
    });
}

// Variables declaration - do not modify                     
private javax.swing.JLabel celsiusLabel;
private javax.swing.JButton convertButton;
private javax.swing.JLabel fahrenheitLabel;
private javax.swing.JTextField tempTextField;
// End of variables declaration                   

}

As you can see, there are 2 jLabels inside this: fahrenheitLabel and celsiusLabel. I've created an auxiliary method dubbed as 'a' that should change the status of fahrenheitLabel to "Working". I'm unable to realize the desired output. Any suggestions?

Answer 1

This is not happening because you are creating another object of class DiligentGUI in your convertButtonActionPerformed method. This is creating another JFrame . You cannot see it coz you did not set it visible by d.setVisible(true) .

Make this change in your

private void convertButtonActionPerformed(java.awt.event.ActionEvent evt) {                                              

    a();  // This will call the a() method in the current running instance. 
    celsiusLabel.setText("Working");
}