AAARGH!!! Can't understand javax.swing.text.*

Question

Good afternoon...
does anybody understand javax.swing.text classes? i've read a number of
books, downloaded docs (including those from the javax.swing.text author), and googled everything i could think of. but nothing seems to explain it to me so that i can understand it! maybe i'm just dense, but maybe it really is that difficult.
i want to create a read-only document, who's source is not necessarily a
string, but perhaps an ArrayList of objects with a HashMap of attributes. or even something simpler for now, just an object with a fixed number of attributes. i want to display this information in a JTextArea. i tried implementing a Document and passing it to the JTextArea constructor but just got a NullPointerException.
does anybody know where i can find more information on creating my own
document types?
here's the code for my ReadOnlyDocument class if anyone of you are generous (& adventurous) enough to take a look:
import java.util.ArrayList;
import javax.swing.event.DocumentListener;
import javax.swing.event.UndoableEditListener;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.Element;
import javax.swing.text.Position;
import javax.swing.text.Segment;
public class ReadOnlyDocument implements Document{
    private String myContent = "this is the contents of my document!";
    private ArrayList listeners;
    private ReadOnlyDocument refSelf = this;
    public ReadOnlyDocument() {
     System.out.println("ReadOnlyDocument.<init>");
    public int getLength() {
     System.out.println("ReadOnlyDocument.getLength() = " + myContent.length());
        return myContent.length();
    public void addDocumentListener(DocumentListener listener) {
     System.out.println("ReadOnlyDocument.addDocumentListener(" + listener + ")");
        if (listeners != null) {
            listeners = new ArrayList();
            listeners.add(listener);
        } else {
            listeners = new ArrayList();
            listeners.add(listener);
    public void removeDocumentListener(DocumentListener listener) {
     System.out.println("ReadOnlyDocument.removeDocumentListener(" +
listener + ")");
        if (listeners != null) {
            listeners.remove(listener);
    public void addUndoableEditListener(UndoableEditListener listener) {
        // Read-only document, nothing to do here
     System.out.println("ReadOnlyDocument.addUndoableEditListener(" +
listener + ")");
    public void removeUndoableEditListener(UndoableEditListener listener) {
        // Read-only document, nothing to do here
     System.out.println("ReadOnlyDocument.removeUndoableEditListener(" +
listener + ")");
    public Object getProperty(Object key) {
        System.out.println("ReadOnlyDocument.getProperty(" + key + ") =
null");
        return null;
    public void putProperty(Object key, Object value) {
           System.out.println("ReadOnlyDocument.putProperty(" + key + ")");
    public void remove(int offs, int len) throws BadLocationException {
        // Read-only document, nothing to do here
     System.out.println("ReadOnlyDocument.remove(" + offs + ", " + len +
    public void insertString(int offset, String str, AttributeSet a) throws
BadLocationException {
        // Read-only document, nothing to do here
     System.out.println("ReadOnlyDocument.insertString(" + offset + ", " +
str + ", " + a + ")");
    public String getText(int offset, int length) throws
BadLocationException {
     System.out.print("ReadOnlyDocument.getText(" + offset + ", " + length +
") = ");
        if ((offset >= 0) && (length >= 0) && (offset+length <=
myContent.length()+1)) {
         System.out.println(myContent.substring(offset, offset+length-1));
            return myContent.substring(offset, offset+length-1);
        } else {
         System.out.println("BadLocationException!");
            throw new BadLocationException("Bad location requested", 0);
    public void getText(int offset, int length, Segment txt) throws
BadLocationException {
     System.out.print("ReadOnlyDocument.getText(" + offset + ", " + length +
", " + txt + ") = ");
        if ((offset >= 0) && (length >= 0) && (offset+length <=
myContent.length()+1)) {
         System.out.println(myContent.substring(offset, offset+length-1));
            txt = new Segment(myContent.toCharArray(), offset, length);
        } else {
         System.out.println("BadLocationException!");
            throw new BadLocationException("Bad location requested", 0);
    public Position getStartPosition() {
     System.out.println("ReadOnlyDocument.getStartPosition() = 0");
  return new Position() {
   public int getOffset() {
    return 0;
    public Position getEndPosition() {
     System.out.println("ReadOnlyDocument.getEndPosition() = " +
myContent.length());
  return new Position() {
   public int getOffset() {
    return myContent.length();
    public Position createPosition(int offs) throws BadLocationException {
     System.out.println("ReadOnlyDocument.createPosition(" + offs + ") =
0");
        if ((offs >= 0) && (offs <= myContent.length()-1)) {
   return new Position() {
    public int getOffset() {
     return 0;
  } else {
   throw new BadLocationException("Bad location requested", 0);
    public Element[] getRootElements() {
     System.out.println("ReadOnlyDocument.getRootElements()");
     Element[] roots = {new Element() {
   public Document getDocument() {
    return refSelf;
   public Element getParentElement() {
    return null;
   public String getName() {
    return "ReadOnlyRoot";
   public AttributeSet getAttributes() {
    return null;
   public int getStartOffset() {
    return 0;
   public int getEndOffset() {
    return myContent.length() - 1;
   public int getElementIndex(int offset) {
    return 0;
   public int getElementCount() {
    return 0;
   public Element getElement(int index) {
    return null;
   public boolean isLeaf() {
    return true;
  return roots;
    public Element getDefaultRootElement() {
     System.out.println("ReadOnlyDocument.getDefaultRootElement()");
  return new Element() {
   public Document getDocument() {
    return refSelf;
   public Element getParentElement() {
    return null;
   public String getName() {
    return "ReadOnlyRoot";
   public AttributeSet getAttributes() {
    return null;
   public int getStartOffset() {
    return 0;
   public int getEndOffset() {
    return myContent.length() - 1;
   public int getElementIndex(int offset) {
    return 0;
   public int getElementCount() {
    return 0;
   public Element getElement(int index) {
    return null;
   public boolean isLeaf() {
    return true;
    public void render(Runnable r) {
        // not sure what to put here
     System.out.println("ReadOnlyDocument.render(" + r + ")");
}and here's a simple class to display the document/generate the error:
import java.awt.event.*;
import javax.swing.*;
public class ReadOnlyFrame extends JFrame {
public ReadOnlyFrame() {
  super();
  setTitle("Read Only Document");
  addWindowListener(new WindowAdapter() {
   public void windowClosed(WindowEvent e) {
    System.exit(0);
  getContentPane().add(new JTextArea(new ReadOnlyDocument()));
  setSize(200, 200);
public static void main(String[] args) {
  ReadOnlyFrame rof = new ReadOnlyFrame();
  rof.setVisible(true);
Headed for the second star to the right and straight on till morning...
Eric Schultz
aka: Storkman
http://community.webshots.com/user/storky1
mailto:EricSchultzATcanadaDOTcom

Answer 1

if you are getting that print before the timer
starts, then I'd expect it's not blocking. The
problem with these small snippets of code is that we
can't really tell what might be going on elsewhere.Yes, I realize that. AAMOF, there isn't anything going on elsewhere, i.e.
the GestureController object spawns another thread when it gets
created. That other thread blocks until a 'Mover' object is delivered to
the GestureController object. The mutex/synchronizing stuff works
like the textbook version, i.e. no deadlock, no deadly embrace, no
nothing. When the timer is started, the Mover is supposed to
call back the 'animate' method, just a method in the GestureController
object.
All the System.out.prints show that it gets there. The task (an ActionListener)
dispatched by that timer doesn't start. As you can see above, I've
used System.out.prints for that too. It is as if that Timer doesn't start.
I still haven't found anything ... This is what the 'auto.move' thing is
supposed to do:     static class DragMover implements Mover {
          DrawableStack from;
          DrawableStack to;
          int position;
          DragMover(DrawableStack from, int position, DrawableStack to) {
               this.from= from;
               this.to  = to;
               this.position= position;
          public void move() {
               System.out.println("moving the stuff...");
               GestureController.getGestureController().animate(from, position, to);
          public void undo() { }          
     }... the line "moving stuff ..." isn't displayed either, i.e. the actionPerformed
method is never called and then ... there's nothing in between there, i.e.
the Timer is supposed to call that method.
Thank you for your reply, much appreciated and,
kind regards,
Jos
by that timer (an ActionListener)