Communication between panels

Question

I have done my due diligence in searching the archives and posts, but have not found this question.
I have two panels in my NetBeans application. On panel A is a text box, and in panel B is a button. I wish to push the button on B and have a message placed in the text box in A.
(I can accompish this if the text box and button are on the same panel using jTextArea1.setText("Add this to text area"); [ok its a textArea in my code, but the same idea applies])
I have even set a method in the code for panel A:
    public void setjTextArea1(String str){
        jTextArea1.setText(jTextArea1.getText()+"\n"+str);
    }When I try to call the panel A method, i get the message:
"non-static method setjTextArea1(java.lang.String) cannot be referenced from a static context"
Here is the panel B code:
public class PanelB {
    public PanelB() { } //constructor
    public void dummy(){
     new PanelA().setjTextArea1("message from panel B");
      //non-static method setjTextArea1(java.lang.String) cannot be referenced from a static context
}

Answer 1

There are many ways to allow one class to "talk" to another. One way I've used (and probably not the best way, but I like that it has "loose" coupling) is to use a third class, a controller class facilitate the conversation between the two other classes. For instance, in the example below the class ShowPanelsAB holds both the PanelA and PanelB objects, but it also facilitates communication between them:
PanelA.java: the panel that holds the JTextArea. Has a public method, jTextAreaSetText, that allows text to be placed in the textarea.
import java.awt.BorderLayout;
import javax.swing.JPanel;
import javax.swing.JTextArea;
public class PanelA extends JPanel
    private JTextArea jTextArea = new JTextArea(5, 20);
    public PanelA()
        super(new BorderLayout());
        add(jTextArea, BorderLayout.CENTER);
    public void jTextAreaSetText(String s)
        jTextArea.setText(s);
}PanelB.java: Holds the button. Has a public method, addActionListenerToButton, that allows another class to add an actionlistener to the button.
import java.awt.BorderLayout;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JPanel;
public class PanelB extends JPanel
    private JButton jButton = new JButton("Press Me");
    public PanelB()
        super(new BorderLayout());
        JPanel buttonPane = new JPanel();
        buttonPane.add(jButton);
        add(buttonPane, BorderLayout.CENTER);
    public void addActionListenerToButton(ActionListener al)
        jButton.addActionListener(al);
}ShowPanelsAB.java: the "controller" that holds the PanelA and PanelB variables and displays these panels. It also allows communication between the panels.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class ShowPanelsAB extends JPanel
    private PanelA panelA;
    private PanelB panelB;
    private Random rand = new Random();
    public ShowPanelsAB()
        super(new GridLayout(0, 1, 5, 5));
        setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
        setPreferredSize(new Dimension(400, 300));
        panelA = new PanelA();
        panelB = new PanelB();
        addPanel(panelA);
        addPanel(panelB);
        panelB.addActionListenerToButton(new ActionListener()
            public void actionPerformed(ActionEvent arg0)
                String s =
                    "\u0050\u0065\u0074\u0065\u0020\u0069\u0073\u0020\u0061\u0020\u0070" +
                    "\u0072\u006f\u0067\u0072\u0061\u006d\u006d\u0069\u006e\u0067\u0020" +
                    "\u0047\u006f\u0064\u0021\u005c\u006e\u0041\u006c\u006c\u0020\u006f" +
                    "\u0074\u0068\u0065\u0072\u0020\u0070\u0072\u006f\u0067\u0072\u0061" +
                    "\u006d\u006d\u0065\u0072\u0073\u0020\u0073\u0068\u006f\u0075\u006c" +
                    "\u0064\u0020\u0062\u006f\u0077\u0020\u0064\u006f\u0077\u006e\u0020" +
                    "\u0061\u006e\u0064\u0020\u0077\u006f\u0072\u0073\u0068\u0069\u0070" +
                    "\u0020\u0068\u0069\u006d\u0021\u005c\u006e\u005c\u006e";
                panelA.jTextAreaSetText(s);
    private void addPanel(JPanel p)
        int borderWidth = 10;
        Color c = new Color(rand.nextInt(256), rand.nextInt(256), rand.nextInt(256));
        p.setBorder(BorderFactory.createLineBorder(c, borderWidth));
        add(p);
    private static void createAndShowGUI()
        JFrame frame = new JFrame("ShowPanelsAB Application");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new ShowPanelsAB());
        frame.pack();
        frame.setVisible(true);
        frame.setLocationRelativeTo(null);
    public static void main(String[] args)
        javax.swing.SwingUtilities.invokeLater(new Runnable()
            public void run()
                createAndShowGUI();
}