How do I Change or Assign a Value to a Private Variable JTextField from another class?

Sorry if this is another stupid-idiotic questions for you, but I'm still a newbie in Java Programming Language.

I have 3 classes: InputClass, PreviewClass, and MainClass.

MainClass contains the main method to run the program. InputClass contains a private JTextField for input and a JButton for setting a text into the JTextField in the PreviewClass. PreviewClass contains a private JTextField to show the inputted text in the InputClass.

How exactly can I do that (assigning value to JTextField in PreviewClass) without creating an instance of the InputClassand then using getter-method-like to obtain the value it has, or, without making JTextField in the InputClass a static variable so I can access it with some static method?

Just to show you my point, here is the code:

1. InputClass

    import javax.swing.*;
    import java.awt.*;
    import java.awt.event.*;
   
    public class InputClass extends JPanel implements ActionListener{
   
        private JTextField inputName;
        private JButton inputButton;
   
        public InputClass() {
            setLayout(new FlowLayout());
   
            inputName=new JTextField(15);
            inputButton=new JButton("INPUT");
            inputButton.addActionListener(this);
   
            add(inputName);
            add(inputButton);
        }
   
        @Override
        public void actionPerformed(ActionEvent event) {
            // How do I change/assign a text to the PreviewClass from here?
        }
   
    }
   

2. PreviewClass

    import javax.swing.*;
    import java.awt.*;
   
    public class PreviewClass extends JPanel{
        private JTextField namePreview;
   
        public PreviewClass() {
             setLayout(new FlowLayout());
   
             namePreview=new JTextField(15);
             namePreview.setEditable(false);
   
             add(namePreview);
        }
   
    }
   

3. MainClass

   import javax.swing.*;
   import java.awt.*;
   
   public class MainClass extends JFrame{
       private static final int FRAME_WIDTH=250;
       private static final int FRAME_HEIGHT=150;
       private static final int FRAME_X_ORIGIN=400;
       private static final int FRAME_Y_ORIGIN=300;
   
       private InputClass inputPanel;
       private PreviewClass previewPanel;
   
       private JTabbedPane tabbedPane;
       private Container contentPane;
   
       public MainClass() {
           contentPane=getContentPane();
           contentPane.setLayout(new BorderLayout());
   
           setTitle("How to Assign Value from Another Class");
           setSize(FRAME_WIDTH, FRAME_HEIGHT);
           setLocation(FRAME_X_ORIGIN, FRAME_Y_ORIGIN);
   
           inputPanel=new InputClass();
           previewPanel=new PreviewClass();
   
           tabbedPane=new JTabbedPane();
           tabbedPane.add("Input Name", inputPanel);
           tabbedPane.add("Preview Name", previewPanel);
   
           contentPane.add(tabbedPane, BorderLayout.CENTER);
   
           setDefaultCloseOperation(EXIT_ON_CLOSE);
       }
   
       public static void main(String[] args) {
           MainClass frame=new MainClass();
           frame.setVisible(true);
       }
   }