Error after compiling because of scroll

Question

I would like to get scrollbars (vertical and horizontal) after doing the Pascal's Triangle that appends in the JTextArea named "prog", inside the JPanel "dret".
I've tried lots of things in teh code, but I get, after compiling:
"Exception in thread "main" java.kang.IllegalArgumentException: adding container's parent to itself
at java.awt.Container.addImpl(Container.java:309)
at java.awt.Container.add(Container.java:210)
at cerni.<init>(cerni.java:218)
at cerni.main(cerni.java:261)
Here the java code:
import java.lang.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.IOException.*;
import javax.swing.text.*;
import java.util.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class cerni extends JFrame {
     //declaraci� de variables.
     JPanel principal, centre, esquerre, dret, intro, esquerrealt, esquerrebaix;
     JButton element2, element3, element4, element6;
     JTextArea prog;
     JTextField element1, element5, introtext;
     static String newline = System.getProperty("line.separator");
     //funci� binominal.     
     public static int binominal (int n, int p) {
          if (p * (n-p) == 0)
               return(1);
          else
               return(binominal(n-1, p-1) + binominal(n-1,p));
     //funci� cerni.
     public cerni() {
          //t�tol.
          super(" �-_JavaPascal_-`");
          //definici� de variables.
          principal = new JPanel();
          centre = new JPanel();
          esquerre = new JPanel();
          dret = new JPanel();
          intro = new JPanel();
          esquerrealt = new JPanel();
          esquerrebaix = new JPanel();     
          element2 = new JButton("Informaci�");
          element4 = new JButton("Fer el triangle");
          element3 = new JButton("Sortir");     
          element6 = new JButton("Netejar la pantalla");          
          element1 = new JTextField("");
          element5 = new JTextField(" Entreu el valor d' n+1 files del triangle de Pascal.");
          introtext = new JTextField(" Benvinguts al programa JavaPascal, el programa escrit i compilat en java que dibuixa el triangle de Pascal.");
          prog = new JTextArea();
          //propietats de texts.
          introtext.setFont(new Font("Serif", Font.ITALIC, 16));          
          prog.setFont(new Font("Serif", Font.ITALIC, 16));
          prog.setLineWrap(true);
          prog.setCaretPosition(prog.getText().length());
          element5.setEditable(false);
          introtext.setEditable(false);
          prog.setEditable(false);
          //minimissatge del principi.          
          JOptionPane.showMessageDialog(principal, " Benvinguts al programa JavaPascal.", " -> Bon dia!! <- ",JOptionPane.INFORMATION_MESSAGE);
          //bot� netejar.
          element6.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e){
                    String o = new String();
                    prog.setText(o);
          //bot� informaci�.
          element2.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e){
                    JOptionPane.showMessageDialog(principal, "El programa JavaPascal ha estat escrit per Cerni Pol durant els dies 11 i 12 de maig del 2002.\nAmb una estructura de JFrame i JPanels, m�s JButtons i components de text, l'aplicaci� en q�esti� us exposar�\nel triangle de Pascal, en tantes files com li demaneu, al camp de text de la dreta.\nNo �s recomanable demanar un n m�s gran de 25, per aix� tenir un millor rendiment en l'operaci� de la compu-\ntadora. (rendiment provat en un processador Pentium2 a 450 mhz)\nQue us ho passeu b� amb aquest programa.\n(Enjoy.)");
          //bot� sortir.
          element3.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e){
                    System.exit (0);
          //bot� pascal.
          element4.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e){
                    int n, p, c;
                    c = 10;
                    String s1 = element1.getText();
                    c = Integer.parseInt(s1);
                    n = 0;
                    p = 0;
                    for (n=0; n<c+1; n++){
                         prog.append(cerni.newline);
                         for (p=0; p<n+1;p++){
                              String s = Integer.toString(binominal (n,p));
                              prog.append(s);
                              prog.append(" ");
               prog.append(cerni.newline);     
          //panell esquerrealt.
          esquerrealt.setLayout(new GridLayout(4, 0));
     esquerrealt.setBorder(BorderFactory.createEmptyBorder(
     30, //top
     20, //left
     40, //bottom
     20) //dret
          esquerrealt.add(element5);
          esquerrealt.add(element4);
          esquerrealt.add(element1);
          esquerrealt.add(element6);
          //panell esquerrebaix.
          esquerrebaix.setLayout(new GridLayout(0, 2));
          esquerrebaix.setBorder(BorderFactory.createEmptyBorder(30, 30, 20, 30));
          esquerrebaix.add(element2);
          esquerrebaix.add(element3);     
          //panell esquerre.
          esquerre.setLayout(new BorderLayout());
          esquerre.add(esquerrealt, "North");
          esquerre.add(esquerrebaix, "South");
          JScrollPane dretScrollPane = new JScrollPane(dret);
          dretScrollPane.createVerticalScrollBar();
          dretScrollPane.createHorizontalScrollBar();          
          dretScrollPane.setVerticalScrollBarPolicy
          (JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);
          dretScrollPane.setHorizontalScrollBarPolicy
          (JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
          dret.add(dretScrollPane);          
          //panell dret.          
          dret.setLayout(new BorderLayout());
          dret.add(prog, "Center");
          //panell centre.
          centre.setPreferredSize(new Dimension(800, 700));
          centre.setBorder(BorderFactory.createEmptyBorder(30, 30, 20, 30));     
          centre.setLayout(new GridLayout(0, 2));
          centre.add(esquerre);
          centre.add(dret);     
          //panell intro.          
          intro.setLayout(new BorderLayout());
          intro.add(introtext, "Center");
          //panell principal.
          principal.setLayout(new BorderLayout());
          principal.setBorder(BorderFactory.createEmptyBorder(30, 30, 20, 30));
          principal.add(centre, "Center");
          principal.add(intro, "North");
          setContentPane(principal);
     //main.     
     public static void main (String[] args) {
          JFrame principal = new cerni();
          principal.addWindowListener (new WindowAdapter () {
               public void windowClosing (WindowEvent e) {System.exit(0);}
     principal.show();
     principal.pack();
     principal.setSize(800, 700);
Thanks to help me.

Answer 1

Hi...
The line is error is below...
dret.add(dretScrollPane);You've already added dret to the scrollpane in the constructor of the scrollpane (some 6/7 lines above the line above). Simply add the scrollpane to the main frame (pane) now.
Merry Christmas