Hi,

Several days ago I asked the same question . Hereby now some code to
explain what I mean.

Working is:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class testinstance extends JFrame{

    JLabel tekst ;
    basis base;
        public testinstance () {

            tekst = new JLabel();
            tekst.setHorizontalAlignment( JLabel.CENTER );
            tekst.setText("not pushed");

            base = new basis(this);;

            Container ContentPane = this.getContentPane();
            GridBagLayout gridbag = new GridBagLayout();
            GridBagConstraints c = new GridBagConstraints();
            ContentPane.setLayout(gridbag);

            c.gridx = 0; c.gridy = 0;
            c.gridheight = 1; c.gridwidth = 5;
            c.weightx = 1; c.weighty = 1;
            c.fill = GridBagConstraints.BOTH;
            ContentPane.add(tekst,c);

            c.gridx = 0; c.gridy = 1;
            c.gridheight = 5; c.gridwidth = 5;
            c.weightx = 2; c.weighty = 2;
            c.fill = GridBagConstraints.BOTH;
            ContentPane.add(base,c);

                    GridLayout gr = new GridLayout(2,0);
                    ContentPane.setLayout(gr);
                    ContentPane.add(tekst);
                    ContentPane.add(base);
            }

    public static void main(String[] args) {
        testinstance f = new testinstance();
              //Display full window.
        Dimension screenSize =
          Toolkit.getDefaultToolkit().getScreenSize();
       f.setSize(screenSize);
       f.setVisible(true);
       f.setDefaultCloseOperation(EXIT_ON_CLOSE);
   }

   public void schrijftekst(String _text) {
     tekst.setText(_text);
   }
}
class basis extends JPanel{

    basis(testinstance ti) {
        GridLayout grid = new GridLayout(3,0);
        setLayout(grid);
        geg g = new geg(ti);
        beta b = new beta();
        this.add(g);
        this.add(b);
    }
}
class geg extends JPanel implements ActionListener {

    JButton knop;
    testinstance ti;

    public geg (testinstance ti) {

        setBackground(Color.green);
        knop = new JButton("Push");

        this.ti = ti;
        FlowLayout fl = new FlowLayout();
        setLayout(fl);
        this.add(knop);
        knop.addActionListener(this);
        }

    public void actionPerformed(ActionEvent e) {
        if(e.getSource() == knop) {
            ti.schrijftekst("Button pushed!");
        }
    }
    public void keyTyped(KeyEvent e) {}
    public void keyReleased(KeyEvent e) {}
}

class beta extends JPanel {
    JButton kn;
    public beta() {
        setBackground(Color.blue);
        kn = new JButton("betabutton");

        FlowLayout flow = new FlowLayout();
        setLayout(flow);
        this.add(kn);
    }
}

When I try to instantiate the classes geg en beta (in 'real life'
public classes)in each other ( to exchange data) I got in trouble in
the main method from the class testinstance . The code:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class testinstance extends JFrame{

    JLabel tekst ;
    private basis base;
        public testinstance (basis ba) {

            tekst = new JLabel();
            tekst.setHorizontalAlignment( JLabel.CENTER );
            tekst.setText("not pushed");

            this.base = ba;

            Container ContentPane = this.getContentPane();
            GridBagLayout gridbag = new GridBagLayout();
            GridBagConstraints c = new GridBagConstraints();
            ContentPane.setLayout(gridbag);

            c.gridx = 0; c.gridy = 0;
            c.gridheight = 1; c.gridwidth = 5;
            c.weightx = 1; c.weighty = 1;
            c.fill = GridBagConstraints.BOTH;
            ContentPane.add(tekst,c);

            c.gridx = 0; c.gridy = 1;
            c.gridheight = 5; c.gridwidth = 5;
            c.weightx = 2; c.weighty = 2;
            c.fill = GridBagConstraints.BOTH;
            ContentPane.add(base,c);

                    GridLayout gr = new GridLayout(2,0);
                    ContentPane.setLayout(gr);
                    ContentPane.add(tekst);
                    ContentPane.add(base);
            }

    public static void main(String[] args) {

        // ' this ' is not allowed in a static !
        //this.base = base;
        //the constructor basis() is undefined
        basis ba = new basis();
        // but, what is the solution?
        testinstance f = new testinstance(ba);
              //Display full window.
        Dimension screenSize =
          Toolkit.getDefaultToolkit().getScreenSize();
       f.setSize(screenSize);
       f.setVisible(true);
       f.setDefaultCloseOperation(EXIT_ON_CLOSE);
   }

   public void schrijftekst(String _text) {
     tekst.setText(_text);
   }
}
class basis extends JPanel{

    basis(testinstance ti, beta be, geg ge) {
        GridLayout grid = new GridLayout(3,0);
        setLayout(grid);
        geg g = new geg(ti, be);
        beta b = new beta(ge);
        this.add(g);
        this.add(b);
    }
}
class geg extends JPanel implements ActionListener {

    JButton knop;
    testinstance ti;
    beta be;
    public geg (testinstance ti, beta be) {

        setBackground(Color.green);
        knop = new JButton("Push");

        this.ti = ti;
        this.be = be;
        FlowLayout fl = new FlowLayout();
        setLayout(fl);
        this.add(knop);
        knop.addActionListener(this);
        }

    public void actionPerformed(ActionEvent e) {
        if(e.getSource() == knop) {
            ti.schrijftekst("Button pushed!");
        }
    }
    public void keyTyped(KeyEvent e) {}
    public void keyReleased(KeyEvent e) {}
}

class beta extends JPanel {
    JButton kn;
    geg ge;
    public beta(geg ge) {
        setBackground(Color.blue);
        kn = new JButton("betabutton");
        this.ge = ge;

        FlowLayout flow = new FlowLayout();
        setLayout(flow);
        this.add(kn);
    }
}

Thanks for helping a newbie,