Help needed refactoring my AutofillTextField

Question

Hello everyone,
Implementing an autofill feature for JTextField raised several design issues, and I would like some help.
First, source code, demo and a diagram can be found on my JRoller entry: http://www.jroller.com/page/handcream?entry=refactoring_challenge_autocomplete_jtextfield
Most difficulties are due to the mix of input and output. I imply what was auto-filled by selecting that part of the text. This affects the input on the other end.
An auto-filled selection doesn't behave like a normal one. Backspace will delete both the selection and an extra character. After that it immediately searches for a match, and auto-fills if necessary.
Adding characters in the middle and getting a match, advances the caret as normal, but also auto-selects the text from that point. So the output "talks" to the input to get the normal caret position.
To intercept text changes in JTextField I override PlainDocument, but other objects need access to the original, super-class methods. For this they use an inner class with methods wrapping the super-class methods.
I wonder if this overriding forces some dirty code, or maybe I can always abstract it away. Maybe I must intercept text changes some other way to make everything cleaner, like removing all keyListeners and add my own. But I doubt that.
My guess is that i'm just unable yet to see the right abstractions, and maybe I didn't go far enough with seperation. Anyway, I need help :). I tried not to ask, but this is going on for too long.
Thanks,
Yonatan.
Some code:
public interface Output {
     void showMatch(String userInput, String fixedInput, String fill);
     void showMismatch(String userInput);
public interface Processor {
     void match(String userInput, Output output);
public interface RealDocument {
     void insertString(int offset, String addition);
     void remove(int offset, int length);
     void clear();
     String getText();
public class AutoFillDocument extends javax.swing.text.PlainDocument {
     @Override
     public void insertString(int offset, java.lang.String addition, javax.swing.text.AttributeSet attributes) throws javax.swing.text.BadLocationException {
          replacing = false;
          String proposedValue = new StringBuilder(real.getText()).insert(offset, addition).toString();
          TextFieldOutput output = new TextFieldOutput(field, real, new DefaultInsert(offset, addition));
          search.match(proposedValue, output);
          autoFilledState = output.autoFilled();
     @Override
     public void remove(int offset, int length) throws javax.swing.text.BadLocationException {
          if (replacing) {
               real.remove(offset, length);
               replacing = false;
          } else {
               removeDirect(offset, length);
     private void removeDirect(int offset, int length) {
          if (backspacing && autoFilledState) {
               offset--;
               length++;
          removeDelegate(offset, length);
     private void removeDelegate(int offset, int length) {
          String proposedValue = new StringBuilder(real.getText()).delete(offset, offset + length).toString();
          TextFieldOutput output = new TextFieldOutput(field, real, new DefaultRemove(offset, length));
          search.match(proposedValue, output);
          autoFilledState = output.autoFilled();
     @Override
     public void replace(int arg0, int arg1, java.lang.String arg2, javax.swing.text.AttributeSet arg3) throws javax.swing.text.BadLocationException {
          replacing = true;
          super.replace(arg0, arg1, arg2, arg3);
     public AutoFillDocument(yon.ui.autofill.Processor search, javax.swing.JTextField field) {
          this.search = search;
          this.field = field;
          field.addKeyListener(new java.awt.event.KeyAdapter() {
               public void keyPressed(java.awt.event.KeyEvent e) {
                    backspacing = java.awt.event.KeyEvent.VK_BACK_SPACE == e.getKeyCode();
     yon.ui.autofill.Processor search;
     javax.swing.JTextField field;
     boolean backspacing = false;
     boolean autoFilledState = false;
     boolean replacing = false;
     public final RealDocument real = new RealDocument();
     private class RealDocument implements yon.ui.autofill.RealDocument {
          public void insertString(int offset, String addition) {
               try {
                    AutoFillDocument.super.insertString(offset, addition, null);
               } catch (Exception ex) {
                    throw new RuntimeException(ex);
          public void remove(int offset, int length) {
               try {
                    AutoFillDocument.super.remove(offset, length);
               } catch (Exception ex) {
                    throw new RuntimeException(ex);
          public void clear() {
               try {
                    AutoFillDocument.super.remove(0, AutoFillDocument.super.getLength());
               } catch (Exception ex) {
                    throw new RuntimeException(ex);
          public String getText() {
               try {
                    return AutoFillDocument.super.getText(0, AutoFillDocument.super.getLength());
               } catch (Exception ex) {
                    throw new RuntimeException(ex);
     private class DefaultInsert implements yon.ui.autofill.TextFieldOutput.DefaultAction {
          public void execute() {
               real.insertString(offset, addition);
          public DefaultInsert(int offset, String addition) {
               this.offset = offset;
               this.addition = addition;
          private int offset;
          private String addition;
     private class DefaultRemove implements yon.ui.autofill.TextFieldOutput.DefaultAction {
          public void execute() {
               real.remove(offset, length);
          public DefaultRemove(int offset, int length) {
               this.offset = offset;
               this.length = length;
          private int offset;
          private int length;
public class DefaultProcessor implements Processor {
     public void match(String userInput, Output output) {
          String match = startsWith(userInput);
          if (match == null) {
               output.showMismatch(userInput);
          } else {
               output.showMatch(userInput, match.substring(0, userInput.length()), match.substring(userInput.length()));
     public String startsWith(String prefix) {
          yon.utils.IsStringPrefix isPrefix = new yon.utils.IsStringPrefix(prefix);
          for (String option: options) {
               if (isPrefix.of(option)) {
                    return option;
          return null;
     public DefaultProcessor(String[] options) {
          this.options = options;
     String[] options;
public class TextFieldOutput implements Output {
     public void showMatch(String userInput, String fixedInput, String fill) {
          if (!userInput.isEmpty()) {
               if (fill.isEmpty()) { // exact match
                    defaultAction.execute();
                    int caretPosition = field.getCaret().getDot();
                    field.getCaret().setDot(fixedInput.length());
                    field.getCaret().moveDot(caretPosition);
               } else {
                    document.clear();
                    document.insertString(0, fixedInput + fill);
                    field.getCaret().setDot(fixedInput.length() + fill.length());
                    field.getCaret().moveDot(fixedInput.length());
               autoFilled = field.getCaret().getDot() != field.getCaret().getMark();
          } else {
               document.clear();
               autoFilled = false;
     public void showMismatch(String userInput) {
          defaultAction.execute();
          autoFilled = false;
     public boolean autoFilled() {
          return autoFilled;
     public TextFieldOutput(javax.swing.JTextField field, yon.ui.autofill.RealDocument document, DefaultAction defaultAction) {
          this.field = field;
          this.document = document;
          this.defaultAction = defaultAction;
     private javax.swing.JTextField field;
     private yon.ui.autofill.RealDocument document;
     private DefaultAction defaultAction;
     private boolean autoFilled;
     public interface DefaultAction {
          void execute();
public class AutoFillFeature {
     public void installIn(javax.swing.JTextField field) {
          Processor processor = new DefaultProcessor(options);
          AutoFillDocument document = new AutoFillDocument(processor, field);
          field.setDocument(document);          
     public AutoFillFeature(String[] options) {
          this.options = options;
     String[] options;
}

Answer 1

I made the code very simple in the interest of discussion in this forum.
1) Now everything is in one class.
2) I extend DocumentFilter instead of Document, which already implements the acrobatics I tried earlier.
3) I Commented most parts of the code.
How would you refactor it? It can be as simple as splitting into more methods, but you can also introduce more objects, and maybe even use a GoF pattern.
Here is the code. Good luck :)
package yon.ui.autofill;
public class AutoFillFilter extends javax.swing.text.DocumentFilter {
     // Called when user tries to insert a string into a text-box.
     // bypass - can change the text without causing a recursion.
     // offset - where to insert
     // addition - what to insert
     // attributes - mostly ignored
     @Override
     public void insertString(FilterBypass bypass, int offset, String addition, javax.swing.text.AttributeSet attributes) throws javax.swing.text.BadLocationException {
          bypass.insertString(offset, addition, attributes);
          handleInput(bypass, currentValue(bypass));
     // Called when user tries to remove a string in a text-box.
     // bypass - can change the text without causing a recursion.
     // offset - where to start removal
     // length - how much to remove
     @Override
     public void remove(FilterBypass bypass, int offset, int length) throws javax.swing.text.BadLocationException {
          if (backspacing && autoFilled) {
               offset--;
               length++;
          bypass.remove(offset, length);
          handleInput(bypass, currentValue(bypass));
     // Called when user tries to replace a string in a text-box.
     // bypass - can change the text without causing a recursion.
     // offset - replaced section start
     // length - replaced section length
     // substitution - ...
     // attributes - mostly ignored
     @Override
     public void replace(FilterBypass bypass, int offset, int length, String substitution, javax.swing.text.AttributeSet attributes) throws javax.swing.text.BadLocationException {
          bypass.remove(offset, length);
          insertString(bypass, offset, substitution, null);
     // Searching for a match and auto-fill.
     // bypass - can change the text without causing a recursion.
     // input - user input
     private void handleInput(FilterBypass bypass, String input) {
          String match = options.firstStartsWith(input);
          handleMatchResult(match, input, bypass);
     // Check match and display in text-box accordingly.
     // match - result from searching options
     // input - raw input from user
     // bypass - can change the text without causing a recursion.
     private void handleMatchResult(String match, String input, FilterBypass bypass) {
          // If no match, or match was default (empty string is prefix of anything)
          //   leave text-box as it is.
          // If matched, imply by selecting the autu-filled section.
          if (match == null || input.isEmpty()) {
               autoFilled = false;
          } else {
               showMatch(bypass, match);
     // Displays text with auto selected section.
     // It knows where to start selecting according to the current caret state.
     private void showMatch(FilterBypass bypass, String match) {
          int caretPosition = field.getCaret().getDot();
          clear(bypass);
          bypassInsertString(bypass, 0, match);
          mark(match.length(), caretPosition);
          autoFilled = field.getCaret().getDot() != field.getCaret().getMark();
     // Convenience method to get the whole text-box text.
     private String currentValue(FilterBypass bypass) {
          try {
               return bypass.getDocument().getText(0, bypass.getDocument().getLength());
          } catch (Exception ex) {
               throw new RuntimeException(ex);
     // Convenience method to insert a string to text-box.
     private void bypassInsertString(FilterBypass bypass, int offset, String addition) {
          try {
               bypass.insertString(offset, addition, null);
          } catch (Exception ex) {
               throw new RuntimeException(ex);
     // Convenience method to clear all text from text-box
     private void clear(FilterBypass bypass) {
          try {
               bypass.remove(0, bypass.getDocument().getLength());
          } catch (Exception ex) {
               throw new RuntimeException(ex);
     // Convenience method to mark (select) a text-box section
     private void mark(int from, int to) {
          field.getCaret().setDot(from);
          field.getCaret().moveDot(to);
     // Constructor
     // Registers a listener to BACKSPACE typing, so we don't just delete a selection,
     //   but delete one extra character. otherwise users can't backspace more than once,
     //   if their input was auto-filled.
     // Registers a listener to text-box caret, so we know if a section of text-box is
     //   selected automatically by us. (it helps together with backspace to delete one
     //   extra character.
     public AutoFillFilter(javax.swing.JTextField field, Options options) {
          this.options = options;
          this.field = field;
          // Similar to C# delegator.
          this.field.addKeyListener(new java.awt.event.KeyAdapter() {
               public void keyPressed(java.awt.event.KeyEvent e) {
                    backspacing = java.awt.event.KeyEvent.VK_BACK_SPACE == e.getKeyCode();
          // Similar to C# delegator.
          field.getCaret().addChangeListener(new javax.swing.event.ChangeListener() {
               public void stateChanged(javax.swing.event.ChangeEvent arg0) {
                    autoFilled = false; // Factory trusts Output to set it only after changing caret, so next caret change fill cancel autofill.
     // Was the current text auto-filled and now in an auto-selection state?
     private boolean autoFilled;
     // Options to match against when trying to auto-fill.
     private Options options;
     // Did the user just pressed Backspace?
     private boolean backspacing = false;
     // The text-box.
     javax.swing.JTextField field;
// One extra class if anyone wants to build and run it.
package yon.ui.autofill;
public class Options {
     public String firstStartsWith(String prefix) {
          yon.utils.IsPrefix isPrefix = new yon.utils.IsPrefix(prefix);
          for (String option: options) {
               if (isPrefix.of(option)) {
                    return option;
          return null;
     public Options(String... options) {
          this.options = options;
     String[] options;
// Oh and this one for prefix checking:
package yon.utils;
public class IsPrefix {
     public boolean of(String str) {
          return str.regionMatches(true, 0, prefix, 0, prefix.length());
     public IsPrefix(String prefix) {
          this.prefix = prefix;
     String prefix;
// And a demo so you have a quick start.
package yon.ui.autofill;
public class MiniApp {
     public static void main(String[] args) {
          javax.swing.SwingUtilities.invokeLater(new Runnable() {
               public void run() {
                    javax.swing.JTextField field = new javax.swing.JTextField();
                    Options options = new Options("English", "Eng12lish", "French", "German", "Heb", "Hebrew");
                    makeAutoFill(field, options);
                    javax.swing.JLabel label = new javax.swing.JLabel("English, Eng12lish, French, German, Heb, Hebrew");
                    javax.swing.JPanel panel = new javax.swing.JPanel();
                    panel.setLayout(new javax.swing.BoxLayout(panel, javax.swing.BoxLayout.PAGE_AXIS));
                    panel.add(field);
                    panel.add(javax.swing.Box.createVerticalStrut(10));
                    panel.add(label);
                    javax.swing.JFrame frame = new javax.swing.JFrame();
                    frame.add(panel);
                    frame.setDefaultCloseOperation(javax.swing.JFrame.EXIT_ON_CLOSE);
                    frame.pack();
                    frame.setVisible(true);
     public static void makeAutoFill(javax.swing.JTextField field, Options options) {
          javax.swing.text.PlainDocument document = new javax.swing.text.PlainDocument();
          document.setDocumentFilter(new AutoFillFilter(field, options));
          field.setDocument(document);     
}