The curious custom panel caper!

Question

Greetings all, before you instantly dismiss this question as too long/noobish, please read it, it's really quite strange. If a couple of you could at least copy the code I have given and let me know if you get the same results that would be great, as I have access to only one machine to program on at the moment.
Anyway, back to the story. I have a curious mystery which is somewhat bizzare. I created a very simple program which features a JButton in a frame which is attached to a JFileChooser. Above the button is a custom JPanel which is basically a fancy text box and is supposed to give the filename of the file selected by the JFileChooser. The weird part comes when you click the button... the component (which is already initialized and has had it's value set) seems to have vanished, its still visible, but trying to change it's value or print any of its attributes results in a NPE. Any ideas you can come up with would be of great help. It's probably something really obvious that my tired eyes just can't spot.
Here is the code... I've stripped it down to the bare minimum to highlight the problem.
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
public class Experiment extends JFrame implements ActionListener{
     private File in_file;
     private JFileChooser fc;
     private JButton button;
     private CustomPanel fileField;
     public Experiment(){
          super("Experiment");
          fc = new JFileChooser();
          JPanel box = new JPanel();
          box.setLayout(new BoxLayout(box,BoxLayout.Y_AXIS));
          box.setBorder(BorderFactory.createTitledBorder(
                           BorderFactory.createEtchedBorder(EtchedBorder.LOWERED),
                           "Form Details"));
          CustomPanel fileLabel = new CustomPanel(CustomPanel.LABEL,"File",250,"file","file");
          fileLabel.setObject("no file selected");
          box.add(fileLabel);
          button = new JButton("Select File");
          button.addActionListener(this);
          button.setActionCommand("select");
          box.add(button);
          getContentPane().add(box, BorderLayout.NORTH);
          setSize(new Dimension(300,120));
          setResizable(false);
          /* this println is successful */
          System.out.println("fileLabel = "+fileLabel.getText());
     public void actionPerformed(ActionEvent e){
          /* this one is unsuccessful! why?! */
          System.out.println("fileField = "+fileField.getText());
          String command = e.getActionCommand();
          if(command.equals("select")){
               selectTemplate();
     public void selectTemplate(){
          int returnVal = fc.showDialog(this, "Select");
        if (returnVal == JFileChooser.APPROVE_OPTION) {
            in_file = fc.getSelectedFile();
               fileField.setObject(in_file.getName());
     public static void main(String [] args) throws IOException{
          Experiment s = new Experiment();
          s.show();
}You will also require the code for the CustomPanel
import java.io.*;
import java.awt.*;
import java.text.*;
import java.util.*;
import javax.swing.*;
public class CustomPanel extends JPanel {
    public static final int TEXT=0;
    public static final int LABEL=1;
    private JPanel spacer;
    private JLabel label,label2;
    private JTextField textField;
    private DisabledCustomPanel disabledField;
    private String entity,labelTxt,toolTip;
    private int type,labelWidth,fieldWidth,maxSize=1024;
    private boolean notNull = false;
     * Creates a new CustomPanel object
     * @param type the type of component to be generated
      * @param labelTxt the text for the label
      * @param labelWidth the width of the label
      * @param fieldWidth the width of the editable field
      * @param entity the entity that this component corresponds to
      * @param toolTip The tool tip text for this component
    public CustomPanel(int type,String labelTxt,int labelWidth,int fieldWidth,String entity,String toolTip){
          this.type=type;
          this.labelTxt=labelTxt;
          this.entity=entity;
          this.toolTip=toolTip;
          this.labelWidth=labelWidth;
          this.fieldWidth=fieldWidth;
          init();
     * Creates a new CustomPanel object
     * @param type the type of component to be generated
      * @param labelTxt the text for the label
      * @param width the width of the entire component (label/field are balanced 3/7)
      * @param entity the entity that this component corresponds to
      * @param toolTip the tool tip text for this component
    public CustomPanel(int type,String labelTxt,int width,String entity,String toolTip){
          this.type=type;
          this.labelTxt=labelTxt;
          this.entity=entity;
          this.toolTip=toolTip;
          labelWidth=(int)((float)width*0.3);
          fieldWidth=(int)((float)width*0.7);
          init();
    private void init() {
          label=new JLabel(labelTxt,SwingConstants.RIGHT);
          setLayout(new FlowLayout(FlowLayout.LEFT,1,3));
          add(label);
          spacer=new JPanel();
          spacer.setPreferredSize(new Dimension(7,7));
          add(spacer);
          disabledField=new DisabledCustomPanel();
          add(disabledField);
          label.setToolTipText(toolTip);
          disabledField.setToolTipText(toolTip);
          switch(type) {
               case TEXT:
                   textField=new JTextField();
                   add(textField);
                   textField.setPreferredSize(new Dimension(fieldWidth,25));
                   break;
               case LABEL:
                   label2=new JLabel("");
                   add(label2);
                   break;
          label.setPreferredSize(new Dimension(labelWidth,25));
          disabledField.setPreferredSize(new Dimension(fieldWidth,25));
          setPreferredSize(new Dimension(labelWidth+fieldWidth,30));
          getActiveComponent().setToolTipText(toolTip);
          setEnabled(false);
     * Returns the contents of the component as a string.
     * @return the String representation of the value held by this component.
    public String getText() {
          Object tmpObj;
          switch(type) {
               case TEXT:
                   return textField.getText().trim();
               case LABEL:
                   return label2.getText().trim();
          return "";
     * Sets the contents of the component.
      * @param obj the object to set.
    public void setObject(Object obj) {
          if (obj == null) {
               clear();
               return;
          String txt=obj.toString();
          switch(type) {
               case TEXT:
                   textField.setText(txt);
                   break;
               case LABEL:
                   label2.setText(txt);
                   break;
          updateDisabled();
     * Updates the field of the component displayed when it is uneditable.
    public void updateDisabled(){
          String txt=getText();
          switch(type){
               case TEXT: case LABEL:
                   disabledField.setText(txt);
                   break;
     * Clears the component's contents.
    public void clear() {
          disabledField.setText("");
          switch(type){
               case TEXT:
                   textField.setText("");break;
               case LABEL:
                   label2.setText("");break;
     * Gets the string you would need to use with an UPDATE statement to
     * represent this component.
     * @return a String consisting of the encapsulated field name and value of
     *         this component in the form <code>field='value'</code> for use
     *         with SQL UPDATE statements.
    public String getUpdateText() {
          switch(type) {
               case LABEL: return "";
          return entity+"='"+formatSQL(getText())+"'";
     * Gets the string you would need to use with an INSERT statement to
     * represent this component.
     * @return a String consisting of the encapsulated value of this component
     *         in the form <code>'value'</code> for use with SQL INSERT
     *         statements.
    public String getInsertText(){
         return "'"+formatSQL(getText())+"'";
     * Gets the type of this CustomPanel.
     * @return the type of this CustomPanel.
    public int getType() {
          return type;
     * Gets the entity currently associated with this CustomPanel.
     * @return the entity currently associated with this CustomPanel.
    public String getEntity() {
          return entity;
     * Creates part of an UPDATE statement given an array of CustomPanel objects.
      * @param v The array of CustomPanel objects to join.
      * @return a textual representation of the set of CustomPanels of the form
      *         <code>field1='value1', field2='value2'</code> used for UPDATE
      *         statements.
    public static String joinForUpdate(CustomPanel [] v) {
          String vStr="";
          int i;
          for (i=0;i<v.length;i++) {
              if (vStr.length() > 0 && v.getType() != LABEL) vStr+=", ";
          vStr+=v[i].getUpdateText();
          return vStr;
* Creates part of an INSERT statement given an array of CustomPanel objects.
     * @param v The array of CustomPanel objects to join.
     * @return a textual representation of the set of CustomPanels of the form
     * <code>'value1', 'value2'</code> used for INSERT statements.
public static String joinForInsert(CustomPanel [] v){
     String vStr="";
     int i;
     for (i=0;i<v.length;i++) {
          if (vStr.length() >0 && v[i].getType() !=LABEL) vStr+=", ";
          vStr+=v[i].getInsertText();
     return vStr;
* Fills in multiple components at once using data from an SQLResult
* object. NB - only the first row from the SQLResult is used.
     * @param v The array of CustomPanel objects
     * @param r The SQLResult containing the destination data
     * @see SQLResult
public static void fill(CustomPanel [] v,SQLResult r) {
          Object tmpObj;
          int i,col;
          for (i=0;i<v.length;i++) {
          col=r.getNamedColumn(v[i].getEntity());
          if (col != -1) {
                    tmpObj=r.getValueAt(0,col);
               if (tmpObj != null) v[i].setObject(tmpObj);
* Sets whether this component may be edited or not.
* @param enabled whether or not you want the component enabled or not.
public void setEnabled(boolean enabled) {
          if (!enabled) updateDisabled();
          getActiveComponent().setVisible(enabled);
          disabledField.setVisible(!enabled);
* Gets the JComponent used by the this CustomPanel to hold data.
* NB - if you change the contents of the component, you will have to
* call updateDisabled().
* @return the JComponent used by this CustomPanel to hold data.
public JComponent getActiveComponent() {
          switch(type) {
          case TEXT:
          return textField;
          case LABEL:
          return label2;
          return null;
* Registers whether this component may be allowed to be NULL (empty).
public void setNotNull(boolean notNull) {
          this.notNull=notNull;
* Registers the maximum number of characters allowed by the component.
* @param maxSize the maximum number of characters allowed by the component.
public void setMaxSize(int maxSize) {
          this.maxSize=maxSize;
* Verifies the integrity constraints of the component.
     * @param usePopup whether to display a popup if there's a problem or not.
     * @return <code>false</code> if the component has a problem,
     * <code>true</code> otherwise.
public boolean verify(boolean usePopup) {
          Object tmpObj;
          switch(type) {
               case TEXT:
               if (notNull && textField.getText().length()==0) {
                    if (usePopup) popup("Please complete the '"+labelTxt+"' field.");
                    return false;
               if (textField.getText().length() > maxSize) {
                    if (usePopup) popup("'"+labelTxt+"' may only contain up to "+
                              maxSize+" characters.");
                    return false;
               break;
          return true;
* Verifies an entire array of components, stopping and popping up an
* error if there's a problem.
     * @param v the target array of CustomPanels to check for validity.
     * @return <code>false</code> if there's a problem, <code>true</code>
     * otherwise.
public static boolean sanityCheck(CustomPanel [] v) {
          int i;
          for (i=0;i<v.length;i++)
          if (!v[i].verify(true)) return false;
          return true;
     * Conveniance method to popup JOptionDialog targeted at this CustomPanel.
     * @param message the message to popup.
     private void popup(String message) {
          JOptionPane.showMessageDialog((JPanel)this,message,"Warning",JOptionPane.WARNING_MESSAGE);
     * Method to format Strings for SQL queries and statements, uses character
     * stuffing to protect special characters.
     * @param txt the String to format.
     * @return the formatted String.
     private static String formatSQL(String txt) {
          String out="";
          String chr;
          int i;
          for (i=0;i<txt.length();i++) {
          chr=""+txt.charAt(i);
          if (chr.equals("'")) chr="''";
          out+=chr;
          return out;
* An easily-readable, un-editable field of text. Used by CustomPanel, but may
* be used alone if necessary.
* @see CustomPanel
public class DisabledCustomPanel extends JPanel{
private JLabel label;
* Creates a new DisabledCustomPanel
public DisabledCustomPanel() {
          super(new GridLayout());
          setBackground(Color.WHITE);
          setForeground(Color.BLACK);
          label=new JLabel();
          label.setFont(new Font("dialog",Font.PLAIN,12));
          add(label);
          setBorder(BorderFactory.createLineBorder(Color.GRAY));
* Sets the text shown by this component.
     * @param txt the text to be shown.
public void setText(String txt) {
          label.setText(" "+txt);
* Sets the tool tip text for this component.
     * @param toolTip the tool tip text for this component.
public void setToolTipText(String toolTip) {
          label.setToolTipText(toolTip);

Answer 1

You are referencing an uninitalized component.
I changed the code below to use the class member var fileField
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
public class Experiment extends JFrame implements ActionListener
    private File in_file;
    private JFileChooser fc;
    private JButton button;
    private CustomPanel fileField;
    public Experiment()
        super("Experiment");
          setDefaultCloseOperation( EXIT_ON_CLOSE );
        fc = new JFileChooser();
        JPanel box = new JPanel();
        box.setLayout(new BoxLayout(box,BoxLayout.Y_AXIS));
        box.setBorder(BorderFactory.createTitledBorder(
                                                      BorderFactory.createEtchedBorder(EtchedBorder.LOWERED),
                                                      "Form Details"));
        //This was a local var that you were using.
       //CustomPanel fileLabel = new CustomPanel(CustomPanel.LABEL,"File",250,"file","file");          
         //You needed to initalize the member var.
        fileField = new CustomPanel(CustomPanel.LABEL,"File",250,"file","file");
        fileField.setObject("no file selected");
        box.add(fileField);
        button = new JButton("Select File");
        button.addActionListener(this);
        button.setActionCommand("select");
        box.add(button);
        getContentPane().add(box, BorderLayout.NORTH);
        setSize(new Dimension(300,120));
        setResizable(false);
        /* this println is successful */
        System.out.println("fileLabel = "+fileField.getText());
    public void actionPerformed(ActionEvent e)
        /* this one is unsuccessful! why?! */
        System.out.println("fileField = "+fileField.getText());
        String command = e.getActionCommand();
        if( command.equals("select") )
            selectTemplate();
    public void selectTemplate()
        int returnVal = fc.showDialog(this, "Select");
        if( returnVal == JFileChooser.APPROVE_OPTION )
            in_file = fc.getSelectedFile();
            fileField.setObject(in_file.getName());
    public static void main(String [] args) throws IOException{
        Experiment s = new Experiment();
        s.show();