In JTabbedPane, I have two panels where same textfield and label are not displayed when written

Question

I wanted to display same textfield and label in both the panels that are added to JTabbedPane but one of panel is displaying the textfield and label and the other is not, when added the same textfield and label for both the panels.

Answer 1

You can only display a component in one container. Better to have your JPanels share the same model, which for the JTextField is its Document, and for the JLabel -- well its text (not really a model that you can extract, so you'll have to change both yourself).

A bit overconvoluted example:

import java.awt.BorderLayout;
import java.awt.Dimension;

import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.event.EventListenerList;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.PlainDocument;

@SuppressWarnings("serial")
public class SharedModels extends JPanel {
    private static final int TABS = 10;
    private JTabbedPane tabbedPane = new JTabbedPane();
    private JTextField labelText = new JTextField(10);
    private MyModel myModel = new MyModel();

    public SharedModels() {
        for (int i = 0; i < TABS; i++) {
            MyPanel myPanel = new MyPanel(myModel);
            String text = "tab: " + (i + 1);
            tabbedPane.addTab(text, myPanel);
        }

        JPanel topPanel = new JPanel();
        topPanel.add(new JLabel("Text for JLabel:"));
        topPanel.add(labelText);
        labelText.getDocument().addDocumentListener(new DocumentListener() {

            @Override
            public void removeUpdate(DocumentEvent e) {
                setLabelText(e);
            }

            @Override
            public void insertUpdate(DocumentEvent e) {
                setLabelText(e);
            }

            @Override
            public void changedUpdate(DocumentEvent e) {
                setLabelText(e);
            }

            private void setLabelText(DocumentEvent e) {
                Document doc = e.getDocument();
                int length = doc.getLength();
                try {
                    String text = doc.getText(0, length);
                    myModel.setLabelText(text);
                } catch (BadLocationException e1) {
                    e1.printStackTrace();
                }
            }
        });

        setLayout(new BorderLayout());
        add(topPanel, BorderLayout.PAGE_START);
        add(tabbedPane, BorderLayout.CENTER);

        add(new MyPanel(myModel), BorderLayout.PAGE_END);
    }

    private static void createAndShowGui() {
        SharedModels mainPanel = new SharedModels();

        JFrame frame = new JFrame("SharedModels");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}

class MyModel {
    private Document document = new PlainDocument();
    private String labelText = "";
    private EventListenerList eventListenerList = new EventListenerList();
    private ChangeEvent changeEvent = null;

    public void addChangeListener(ChangeListener l) {
        eventListenerList.add(ChangeListener.class, l);
    }

    public void removeChangeListener(ChangeListener l) {
        eventListenerList.remove(ChangeListener.class, l);
    }

    public String getLabelText() {
        return labelText;
    }

    public void setLabelText(String labelText) {
        this.labelText = labelText;
        fireChangeListeners();
    }

    protected void fireChangeListeners() {
        Object[] listeners = eventListenerList.getListenerList();
        for (int i = listeners.length-2; i>=0; i-=2) {
            if (listeners[i] == ChangeListener.class) {
                if (changeEvent == null) {
                    changeEvent = new ChangeEvent(this);
                }
                ((ChangeListener) listeners[i + 1]).stateChanged(changeEvent);
            }
        }
    }

    public Document getDocument() {
        return document;
    }
}

@SuppressWarnings("serial")
class MyPanel extends JPanel {
     private JLabel label = new JLabel("");
     private JTextField textField = new JTextField(10);

    public MyPanel(MyModel myModel) {
        textField.setDocument(myModel.getDocument());
        myModel.addChangeListener(ce -> {
            label.setText(myModel.getLabelText());
        });

        add(new JLabel("Label text:"));
        add(label);
        add(textField);
        setPreferredSize(new Dimension(400, 100));
    }     

}