How can I access data in different panels?

Question

Hi,
I'm a beginner in Swing and have a simple(?) question. Unfortunately I didn't find the answer by oneself so I hope you can help me.
I have three classes. In the GUI.java class I build the JFrame and it's components. All components are added to the frame via panels that a separate classes.
My problem is: how can I acces the values in PanelB when I call the actionPerfomed in PanelA? Or is that always a bad design? How can I make it better?
GUI.java
JFrame frame = new JFrame();
PanelA panelA = new PanelA();
PanelB panelB = new PanelB();
frame.getContentPane().add(panelA);
frame.getContentPane().add(panelB);PanelA.java
private class ButtonCalculateAction implements ActionListener {
     public void actionPerformed(ActionEvent e){
          //calculate with valuesX and valuesY from Panel B
JButton buttonCalculate;
...PanelB.java
JList valuesX;
JList valuesY;
JButton addValueX;
...

Answer 1

Here is the code for a Short, Self Contained, Correct (Compilable), Example
GUI.java
import java.awt.FlowLayout;
import javax.swing.JFrame;
public class GUI {
     public GUI(){
          JFrame frame = new JFrame();
          PanelA panelA = new PanelA();
          PanelB panelB = new PanelB();
          frame.getContentPane().setLayout(new FlowLayout());
          frame.getContentPane().add(panelA);
          frame.getContentPane().add(panelB);
          frame.setSize(400, 200);
          frame.setVisible(true);
     public static void main(String[] args) {
          GUI gui = new GUI();
}PanelA.javaimport java.awt.event.*;
import javax.swing.*;
import java.awt.*;
public class PanelA extends JPanel {
     public PanelA(){
          this.setLayout(new FlowLayout());
          this.buttonCalculate = new JButton("Calculate");
          this.buttonCalculate.addActionListener(new ButtonCalculateAction());
          this.add(buttonCalculate);
          this.result = new JTextField("...");
          this.add(result);
     private class ButtonCalculateAction implements ActionListener {
          public void actionPerformed(ActionEvent e){
               //calculate with values from PanelB. How??
               //result = ?
     private JButton buttonCalculate;
     private JTextField result;
}PanelB.java
import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
public class PanelB extends JPanel {
     public PanelB(){
          this.addValueX = new JButton("Add X");
          this.addValueX.addActionListener(new ButtonAddAction());
          this.valuesXList = new DefaultListModel();
          this.valuesX = new JList();
          this.valuesX.setModel(valuesXList);
          this.add(addValueX);
          this.add(valuesX);
     private class ButtonAddAction implements ActionListener {
          public void actionPerformed(ActionEvent e){
               valuesXList.addElement(47);
     private JList valuesX;
     private DefaultListModel valuesXList;
     private JButton addValueX;
}