Change jLable-text from another class

Question

My problem: I can't change the text of a jLabel from an other class. In my JFrame-Class, which is called "NewJFrame" I have defined a method called "setLabelText()" in which the text of jLable1 is changed. This method is called from the main-Method, but the text doesn't change. What's wrong? would be very grateful for help!

public class Main {

    static NewJFrame f = new NewJFrame();

    public static void main(String[] args) {

        f.main(null);
        f.setLabelText("changedText");

    }

}

and here my new JFrame class with a lot of generated stuff in there. The important thing is the setText()-Method.

 public class NewJFrame extends javax.swing.JFrame {


    public NewJFrame() {
        initComponents();
    }


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

        jLabel1 = new javax.swing.JLabel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jLabel1.setText("jLabel1");

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(156, 156, 156)
                .addComponent(jLabel1)
                .addContainerGap(203, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addContainerGap(152, Short.MAX_VALUE)
                .addComponent(jLabel1)
                .addGap(132, 132, 132))
        );

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



    public static void main(String args[]) {

        //<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(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }



        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new NewJFrame().setVisible(true);
            }
        });
    }


    public void setLabelText (String text){
        jLabel1.setText(text);

    }



    // Variables declaration - do not modify                     
    private javax.swing.JLabel jLabel1;
    // End of variables declaration                   
}

Answer 1

I need to call the setText()-method from Main-class

What is the purpose of f.main(null); and you are trying to set text to the JFrame in this line: f.setText("changedText");

As a solution, change your JLabel access modifier to public. By default it is private, because of that you cannot change it in another class.

Change:

private javax.swing.JLabel jLabel1;

To:

public javax.swing.JLabel jLabel1;

In netbenas you cannot edit generated codes by default. So to change access modifier, right click on the JLabel in design window* and go to the customize code. In that window change the Access: to public.

Now, change the Main class as below:

public class Main {
    static NewJFrame f = new NewJFrame();

    public static void main(String[] args) {
        f.jLabel1.setText("changedText");//this line will get the label in NewJFrame and set the text
        //f.setVisible(true);//this is added to open the frame. May be you dont want this line
    }
}

Answer 2

When you create JFrame frame (from netbeans) it already have its main function in it. so either you have to create JPanel and manually initialize in your class having main function, or you can move f.setText("XYZ"); to the NewJFrame() class. It would be like :

public static void main(String args[]) {

        //<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(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }



        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                ***NewJFrame f=new NewJFrame();
f.setVisible(true);
f.setText("Your Text Goes Here");***
            }
        });
    }