We Keep Coding

JTextField take twice the input, but why?

I wanna make a programmable calculator, i got the basic GUI, and now i'm trying to set up the buttons, and the display. My display text will be "0" basically and if the user type in a number, that number should to be displayed. I tried to do it with KeyListener, but if i press a key it will display the key twice. Why?
textField.addKeyListener(new KeyListener(){
boolean newNumber = true;
public void keyTyped(KeyEvent e) {
}
public void keyPressed(KeyEvent e) {
int keyCode = e.getKeyCode();
if(keyCode == e.VK_BACK_SPACE && textField.getText().length() == 1){
textField.setText("0");
newNumber = true;
}
if(textField.getText().equals("0") && newNumber){
textField.setText(KeyEvent.getKeyText(keyCode));
newNumber = false;
}
}
public void keyReleased(KeyEvent e) {
}
});
Before input:
After "1" input:

Here a simple solution:
If you use keyPressed, you have to do something in keyReleased and this become
complicated. keyTyped is a more simple way.
You can use e.consume() to prevent having the double digit inserted.
textField.addKeyListener(new KeyListener() {
int codeDelete = KeyEvent.getExtendedKeyCodeForChar(KeyEvent.VK_DELETE);
int codeBackSpace = KeyEvent.getExtendedKeyCodeForChar(KeyEvent.VK_BACK_SPACE);
#Override
public void keyTyped(KeyEvent e) {
char keyChar = e.getKeyChar();
if (textField.getText().length() == 0) {
textField.setText("0");
}
else if (textField.getText().equals("0") && keyChar != codeDelete && keyChar != codeBackSpace) {
textField.setText(String.valueOf(e.getKeyChar()));
e.consume();
}
}
#Override
public void keyPressed(KeyEvent e) {
}
#Override
public void keyReleased(KeyEvent e) {
}
});

For doing that, I derive PlainDocument like this:
import java.awt.EventQueue;
import java.util.regex.Pattern;
import javax.swing.JTextField;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.PlainDocument;
public class DigitDocument extends PlainDocument {
private static final long serialVersionUID = 1L;
protected static final Pattern patternStartZero = Pattern.compile("^0.+");
protected final JTextField textField;
private final int limit;
private final Runnable runnableFormat;
public DigitDocument(JTextField textField, int limit) {
super();
this.textField = textField;
this.limit = limit;
runnableFormat = new Runnable() {
#Override
public void run() {
String text = textField.getText();
if (text.length() == 0) {
textField.setText("0");
}
else if (patternStartZero.matcher(text).matches()) {
textField.setText(text.replaceAll("^0+", ""));
}
}
};
}
#Override
public void insertString(int offset, String str, AttributeSet attr) throws BadLocationException {
str = str.replaceAll("[^0-9]", "");
if (str.length() == 0)
return;
else if ((getLength() + str.length()) <= limit)
super.insertString(offset, str, attr);
EventQueue.invokeLater(runnableFormat);
}
#Override
public void remove(int offs, int len) throws BadLocationException {
if (!"0".equals(textField.getText()))
super.remove(offs, len);
EventQueue.invokeLater(runnableFormat);
}
}
The usage is:
textField.setDocument(new DigitDocument(textField, 10));
textField.setText("0");
In DigitDocument,
First arg is the JTextField himself.
Second arg (10) is the maximum input length,
You can enter only digit.

KeyEvent Handler help - JAVA [duplicate]

I have the following code
import javax.swing.*;
import java.awt.*;
import net.miginfocom.swing.MigLayout;
import Sorts.*;
import javax.swing.event.*;
import java.awt.event.*;
import java.awt.Color;
public class SortsGui
{
JFrame myMainWindow = new JFrame("Sorts");
JPanel sortPanel = new JPanel();
//first panel components
public int nextTextBox = 20;
JTextField[] allField = new JTextField [25];
//end first panel
public void runGUI()
{
myMainWindow.setBounds(10, 10, 800, 800);
myMainWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
myMainWindow.setLayout(new GridLayout(1,1));
createSortTestPanel();
myMainWindow.getContentPane().add(sortPanel);
myMainWindow.setVisible(true);
}
public void createSortTestPanel()
{
MigLayout layout = new MigLayout("" , "[grow]");
sortPanel.setLayout(layout);
refreshScreen();
}
public void refreshScreen()
{
sortPanel.removeAll();
for(int i = 0; i<nextTextBox;i++)
{
int fix = i+1;
allField[i] = new JTextField("");
sortPanel.add(allField[i],"growx");
allField[i].addKeyListener(new KeyListener ()
{
public void keyPressed(KeyEvent e)
{
}
public void keyReleased(KeyEvent e)
{
}
public void keyTyped(KeyEvent e)
{
char c = e.getKeyChar();
if(Character.isDigit(c))
{
}
else
{
e.consume();
}
try
{
int parseTest = Integer.parseInt(allField[i].getText());
}
catch(Exception exc)
{
allField[i].setBackground(Color.RED);
}
}
});
}
}
public static void main(String[] args)
{
SortsGui sG = new SortsGui();
sG.runGUI();
}
}
My aim here is to create an array of JTextFields which have a keylistener on. This keylistener should prevent anything other than numbers being entered in the JTextField. It should also change the color of the JTextField's background if the number entered is not an int. For example 2147483647554.
However when I compile this I get the error
So how do I make this so that it is either final or effectively final on all the JTextFields?

My aim here is to create an array of JTextFields which have a keylistener on. This keylistener should prevent anything other than numbers being entered in the JTextField
The short answer to this is, don't use KeyListener, it won't capture the use cases of the user pasting text into the field or if the field is updated programmatically
Instead you want to use a DocumentFilter, for example
public class IntFilter extends DocumentFilter {
#Override
public void insertString(DocumentFilter.FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException {
StringBuilder buffer = new StringBuilder(text.length());
for (int index = 0; index < text.length(); index++) {
if (Character.isDigit(text.charAt(index))) {
buffer.append(text.charAt(index));
}
}
super.insertString(fb, offset, buffer.toString(), attr);
ValidationListener listener = getValidationListener();
}
#Override
public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String string, AttributeSet attr) throws BadLocationException {
if (length > 0) {
fb.remove(offset, length);
}
insertString(fb, offset, string, attr);
}
}
See Implementing a Document Filter for more details and DocumentFilter Examples for more examples
It should also change the color of the JTextField's background if the number entered is not an int
You can do post validation using a InputVerifier, but that might not meet your needs.
This creates a problem. The DocumentFilter, shouldn't care about the field it's applied to, but since, it's doing the validation, it will know when something has gone wrong, so we need some way for the filter to provide notification when the validation fails...
First, we need some callback which tells us when validation has failed or passed...
public interface ValidationListener {
public void validationFailed();
public void validationPassed();
}
Then we need to update the filter to raise those notifications based on it's rules...
public class IntFilter extends DocumentFilter {
private ValidationListener validationListener;
public void setValidationListener(ValidationListener validationListener) {
this.validationListener = validationListener;
}
public ValidationListener getValidationListener() {
return validationListener;
}
#Override
public void insertString(DocumentFilter.FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException {
boolean validationFailed = false;
StringBuilder buffer = new StringBuilder(text.length());
for (int index = 0; index < text.length(); index++) {
if (Character.isDigit(text.charAt(index))) {
buffer.append(text.charAt(index));
} else {
validationFailed = true;
}
}
super.insertString(fb, offset, buffer.toString(), attr);
ValidationListener listener = getValidationListener();
if (listener != null) {
if (validationFailed) {
listener.validationFailed();
} else {
listener.validationPassed();
}
}
}
#Override
public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String string, AttributeSet attr) throws BadLocationException {
if (length > 0) {
fb.remove(offset, length);
}
insertString(fb, offset, string, attr);
}
}
Then we need to define our implementation of the ValidationListener to perform the actions we need...
public class DefaultValidationHandler implements ValidationListener {
private JTextField field;
public DefaultValidationHandler(JTextField field) {
this.field = field;
}
public JTextField getField() {
return field;
}
#Override
public void validationFailed() {
getField().setBackground(Color.RED);
}
#Override
public void validationPassed() {
getField().setBackground(UIManager.getColor("TextField.background"));
}
}
Here, the listener maintains a reference to the field which we want to control
Then we bind it altogether...
JTextField field = new JTextField(10);
DefaultValidationHandler handler = new DefaultValidationHandler(field);
IntFilter filter = new IntFilter();
filter.setValidationListener(handler);
((AbstractDocument)field.getDocument()).setDocumentFilter(filter);
This is all a bit crude, but it gets the basic idea across.
Some improvements might include passing the reference of the DocumentFilter back via the methods of the ValidationListener, you could then use this to lookup the field which triggered the event and update it, reducing the number of handlers you might need to create, for example.
For example
Updated ValidationListener
public interface ValidationListener {
public void validationFailed(DocumentFilter filter);
public void validationPassed(DocumentFilter filter);
}
Updated IntFilter
public class IntFilter extends DocumentFilter {
private ValidationListener validationListener;
public void setValidationListener(ValidationListener validationListener) {
this.validationListener = validationListener;
}
public ValidationListener getValidationListener() {
return validationListener;
}
#Override
public void insertString(DocumentFilter.FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException {
boolean validationFailed = false;
StringBuilder buffer = new StringBuilder(text.length());
for (int index = 0; index < text.length(); index++) {
if (Character.isDigit(text.charAt(index))) {
buffer.append(text.charAt(index));
} else {
validationFailed = true;
}
}
super.insertString(fb, offset, buffer.toString(), attr);
ValidationListener listener = getValidationListener();
if (listener != null) {
if (validationFailed) {
listener.validationFailed(this);
} else {
listener.validationPassed(this);
}
}
}
#Override
public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String string, AttributeSet attr) throws BadLocationException {
if (length > 0) {
fb.remove(offset, length);
}
insertString(fb, offset, string, attr);
}
}
Example implementation...
public class TestPane extends JPanel {
private Map<DocumentFilter, JTextField> fields;
public TestPane() {
fields = new HashMap<>(25);
ValidationListener listener = new ValidationListener() {
#Override
public void validationFailed(DocumentFilter filter) {
JTextField field = fields.get(filter);
if (field != null) {
field.setBackground(Color.RED);
}
}
#Override
public void validationPassed(DocumentFilter filter) {
JTextField field = fields.get(filter);
if (field != null) {
field.setBackground(UIManager.getColor("TextField.background"));
}
}
};
setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.gridwidth = GridBagConstraints.REMAINDER;
for (int index = 0; index < 10; index++) {
JTextField field = new JTextField(10);
IntFilter filter = new IntFilter();
filter.setValidationListener(listener);
((AbstractDocument) field.getDocument()).setDocumentFilter(filter);
fields.put(filter, field);
add(field, gbc);
}
}
}

You have a scoping issue that's why getting this error:
for(int i = 0; i<nextTextBox;i++) //you are declaring i here
using inside KeyListener , This is prohibited. Because local non-final variable cant be accessed from inner class to access it must be final. In your case I don't think it is possible to make i final
So, one quick fix is declare i in the class scope with the JFrame and JPanel
JFrame myMainWindow = new JFrame("Sorts");
JPanel sortPanel = new JPanel();
int i;
then use it any where
for(i = 0; i<nextTextBox;i++)

Referencing from an inner class

I have the following code
import javax.swing.*;
import java.awt.*;
import net.miginfocom.swing.MigLayout;
import Sorts.*;
import javax.swing.event.*;
import java.awt.event.*;
import java.awt.Color;
public class SortsGui
{
JFrame myMainWindow = new JFrame("Sorts");
JPanel sortPanel = new JPanel();
//first panel components
public int nextTextBox = 20;
JTextField[] allField = new JTextField [25];
//end first panel
public void runGUI()
{
myMainWindow.setBounds(10, 10, 800, 800);
myMainWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
myMainWindow.setLayout(new GridLayout(1,1));
createSortTestPanel();
myMainWindow.getContentPane().add(sortPanel);
myMainWindow.setVisible(true);
}
public void createSortTestPanel()
{
MigLayout layout = new MigLayout("" , "[grow]");
sortPanel.setLayout(layout);
refreshScreen();
}
public void refreshScreen()
{
sortPanel.removeAll();
for(int i = 0; i<nextTextBox;i++)
{
int fix = i+1;
allField[i] = new JTextField("");
sortPanel.add(allField[i],"growx");
allField[i].addKeyListener(new KeyListener ()
{
public void keyPressed(KeyEvent e)
{
}
public void keyReleased(KeyEvent e)
{
}
public void keyTyped(KeyEvent e)
{
char c = e.getKeyChar();
if(Character.isDigit(c))
{
}
else
{
e.consume();
}
try
{
int parseTest = Integer.parseInt(allField[i].getText());
}
catch(Exception exc)
{
allField[i].setBackground(Color.RED);
}
}
});
}
}
public static void main(String[] args)
{
SortsGui sG = new SortsGui();
sG.runGUI();
}
}
My aim here is to create an array of JTextFields which have a keylistener on. This keylistener should prevent anything other than numbers being entered in the JTextField. It should also change the color of the JTextField's background if the number entered is not an int. For example 2147483647554.
However when I compile this I get the error
So how do I make this so that it is either final or effectively final on all the JTextFields?

My aim here is to create an array of JTextFields which have a keylistener on. This keylistener should prevent anything other than numbers being entered in the JTextField
The short answer to this is, don't use KeyListener, it won't capture the use cases of the user pasting text into the field or if the field is updated programmatically
Instead you want to use a DocumentFilter, for example
public class IntFilter extends DocumentFilter {
#Override
public void insertString(DocumentFilter.FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException {
StringBuilder buffer = new StringBuilder(text.length());
for (int index = 0; index < text.length(); index++) {
if (Character.isDigit(text.charAt(index))) {
buffer.append(text.charAt(index));
}
}
super.insertString(fb, offset, buffer.toString(), attr);
ValidationListener listener = getValidationListener();
}
#Override
public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String string, AttributeSet attr) throws BadLocationException {
if (length > 0) {
fb.remove(offset, length);
}
insertString(fb, offset, string, attr);
}
}
See Implementing a Document Filter for more details and DocumentFilter Examples for more examples
It should also change the color of the JTextField's background if the number entered is not an int
You can do post validation using a InputVerifier, but that might not meet your needs.
This creates a problem. The DocumentFilter, shouldn't care about the field it's applied to, but since, it's doing the validation, it will know when something has gone wrong, so we need some way for the filter to provide notification when the validation fails...
First, we need some callback which tells us when validation has failed or passed...
public interface ValidationListener {
public void validationFailed();
public void validationPassed();
}
Then we need to update the filter to raise those notifications based on it's rules...
public class IntFilter extends DocumentFilter {
private ValidationListener validationListener;
public void setValidationListener(ValidationListener validationListener) {
this.validationListener = validationListener;
}
public ValidationListener getValidationListener() {
return validationListener;
}
#Override
public void insertString(DocumentFilter.FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException {
boolean validationFailed = false;
StringBuilder buffer = new StringBuilder(text.length());
for (int index = 0; index < text.length(); index++) {
if (Character.isDigit(text.charAt(index))) {
buffer.append(text.charAt(index));
} else {
validationFailed = true;
}
}
super.insertString(fb, offset, buffer.toString(), attr);
ValidationListener listener = getValidationListener();
if (listener != null) {
if (validationFailed) {
listener.validationFailed();
} else {
listener.validationPassed();
}
}
}
#Override
public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String string, AttributeSet attr) throws BadLocationException {
if (length > 0) {
fb.remove(offset, length);
}
insertString(fb, offset, string, attr);
}
}
Then we need to define our implementation of the ValidationListener to perform the actions we need...
public class DefaultValidationHandler implements ValidationListener {
private JTextField field;
public DefaultValidationHandler(JTextField field) {
this.field = field;
}
public JTextField getField() {
return field;
}
#Override
public void validationFailed() {
getField().setBackground(Color.RED);
}
#Override
public void validationPassed() {
getField().setBackground(UIManager.getColor("TextField.background"));
}
}
Here, the listener maintains a reference to the field which we want to control
Then we bind it altogether...
JTextField field = new JTextField(10);
DefaultValidationHandler handler = new DefaultValidationHandler(field);
IntFilter filter = new IntFilter();
filter.setValidationListener(handler);
((AbstractDocument)field.getDocument()).setDocumentFilter(filter);
This is all a bit crude, but it gets the basic idea across.
Some improvements might include passing the reference of the DocumentFilter back via the methods of the ValidationListener, you could then use this to lookup the field which triggered the event and update it, reducing the number of handlers you might need to create, for example.
For example
Updated ValidationListener
public interface ValidationListener {
public void validationFailed(DocumentFilter filter);
public void validationPassed(DocumentFilter filter);
}
Updated IntFilter
public class IntFilter extends DocumentFilter {
private ValidationListener validationListener;
public void setValidationListener(ValidationListener validationListener) {
this.validationListener = validationListener;
}
public ValidationListener getValidationListener() {
return validationListener;
}
#Override
public void insertString(DocumentFilter.FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException {
boolean validationFailed = false;
StringBuilder buffer = new StringBuilder(text.length());
for (int index = 0; index < text.length(); index++) {
if (Character.isDigit(text.charAt(index))) {
buffer.append(text.charAt(index));
} else {
validationFailed = true;
}
}
super.insertString(fb, offset, buffer.toString(), attr);
ValidationListener listener = getValidationListener();
if (listener != null) {
if (validationFailed) {
listener.validationFailed(this);
} else {
listener.validationPassed(this);
}
}
}
#Override
public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String string, AttributeSet attr) throws BadLocationException {
if (length > 0) {
fb.remove(offset, length);
}
insertString(fb, offset, string, attr);
}
}
Example implementation...
public class TestPane extends JPanel {
private Map<DocumentFilter, JTextField> fields;
public TestPane() {
fields = new HashMap<>(25);
ValidationListener listener = new ValidationListener() {
#Override
public void validationFailed(DocumentFilter filter) {
JTextField field = fields.get(filter);
if (field != null) {
field.setBackground(Color.RED);
}
}
#Override
public void validationPassed(DocumentFilter filter) {
JTextField field = fields.get(filter);
if (field != null) {
field.setBackground(UIManager.getColor("TextField.background"));
}
}
};
setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
gbc.gridwidth = GridBagConstraints.REMAINDER;
for (int index = 0; index < 10; index++) {
JTextField field = new JTextField(10);
IntFilter filter = new IntFilter();
filter.setValidationListener(listener);
((AbstractDocument) field.getDocument()).setDocumentFilter(filter);
fields.put(filter, field);
add(field, gbc);
}
}
}

You have a scoping issue that's why getting this error:
for(int i = 0; i<nextTextBox;i++) //you are declaring i here
using inside KeyListener , This is prohibited. Because local non-final variable cant be accessed from inner class to access it must be final. In your case I don't think it is possible to make i final
So, one quick fix is declare i in the class scope with the JFrame and JPanel
JFrame myMainWindow = new JFrame("Sorts");
JPanel sortPanel = new JPanel();
int i;
then use it any where
for(i = 0; i<nextTextBox;i++)

Get a key from JTextArea

All I want to do, If I'm pressing '{' this key in JtextArea.automatically '}' this will be print also.
if(evt.KEY_PRESSED == '{')
System.out.print("}");
is this is okay??

for listening changes into JTextComponent is there DocumentListener, if you have to need control over inputed Char, sings, whitespace chars or word(s) you have to implements DocumentFilter
notice for Chars reservated by programing language(s) you have to use double escapes,
\\( instead of (
or
\\{ instead of {
otherwise you get
Exception in thread "AWT-EventQueue-0" java.util.regex.PatternSyntaxException:
Illegal repetition
for example
import java.awt.*;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
public class TextAreaTest extends JFrame {
private static final long serialVersionUID = 1L;
private JTextArea textArea;
public TextAreaTest() {
textArea = new JTextArea();
textArea.setPreferredSize(new Dimension(60, 32));
textArea.setOpaque(true);
textArea.setLineWrap(true);
textArea.setWrapStyleWord(true);
((AbstractDocument) textArea.getDocument()).setDocumentFilter(new DocumentFilter() {
#Override
public void insertString(FilterBypass fb, int offset, String string, AttributeSet attr) throws BadLocationException {
string = string.replaceAll("\\{", "\\{}");
super.insertString(fb, offset, string, attr);
}
#Override
public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
text = text.replaceAll("\\{", "\\{}");
//TODO must do something here
super.replace(fb, offset, length, text, attrs);
}
});
textArea.getDocument().addDocumentListener(new DocumentListener() {
#Override
public void changedUpdate(DocumentEvent e) {
update(e);
}
#Override
public void insertUpdate(DocumentEvent e) {
update(e);
}
#Override
public void removeUpdate(DocumentEvent e) {
update(e);
}
private void update(DocumentEvent e) {
List<String> lines = getLines(textArea);
String lastLine = lines.get(lines.size() - 1);
int tabbedTextWidth = Utilities.getTabbedTextWidth(new Segment(
lastLine.toCharArray(), 0, lastLine.length()), textArea.getFontMetrics(textArea.getFont()), 0, null, 0);
int lineHeight = getLineHeight(textArea);
if (lines.size() * lineHeight > textArea.getHeight() || tabbedTextWidth > textArea.getWidth()) {
System.out.println("Too big! Should refuse the update!");
}
}
});
getContentPane().add(textArea);
}
private static List<String> getLines(JTextArea textArea) {
int lineHeight = getLineHeight(textArea);
List<String> list = new ArrayList<String>();
for (int num = 0;; num++) {
int i = textArea.viewToModel(new Point(0, num * lineHeight));
int j = textArea.viewToModel(new Point(0, (num + 1) * lineHeight));
if (i == 0 && j == 0) {
continue;
}
if (textArea.getDocument().getLength() == i && i == j) {
break;
}
String s = removeTrailingNewLine(textArea.getText().substring(i, j));
list.add(s);
//System.out.println(i + " " + j + " = " + s);
}
return list;
}
private static int getLineHeight(JTextArea textArea) {
return textArea.getFontMetrics(textArea.getFont()).getHeight();
}
private static String removeTrailingNewLine(String s) {
if (s.endsWith("\n")) {
return s.substring(0, s.length() - 1);
} else {
return s;
}
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
TextAreaTest test = new TextAreaTest();
test.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
test.pack();
test.setVisible(true);
}
});
}
}

You need KeyBinding
http://tips4java.wordpress.com/2008/10/10/key-bindings/
and
http://docs.oracle.com/javase/tutorial/uiswing/misc/keybinding.html

I think this is what you are looking for
if(evt.getID() == evt.KEY_PRESSED) {
if(evt.getKeyChar() == '{') {
System.out.print("}");
}
}
Tested and works

How do I limit the amount of characters in JTextPane as the user types (Java)

I need to not allow any characters to be entered after X have been typed. I need to send a beep after X characters have been typed. I know how to do this after the user presses enter, but I need to do it before the user presses enter. The approach I found from Oracle's site is to add a DocumentSizeFilter to the JTextPane. I can't get this to notify the user when they have gone over (it doesn't work until they press enter). This is a sample of what I have.
public class EndCycleTextAreaRenderer extends JTextPane
implements TableCellRenderer {
private final int maxNumberOfCharacters = 200;
public EndCycleTextAreaRenderer() {
StyledDocument styledDoc = this.getStyledDocument();
AbstractDocument doc;
doc = (AbstractDocument)styledDoc;
doc.setDocumentFilter(new DocumentSizeFilter(maxNumberOfCharacters ));
}

Override the insertString method of the document in the JTextPane so that it doesn't insert any more characters once the maximum has been reached.
For example:
JTextPane textPane = new JTextPane(new DefaultStyledDocument() {
#Override
public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
if ((getLength() + str.length()) <= maxNumberOfCharacters) {
super.insertString(offs, str, a);
}
else {
Toolkit.getDefaultToolkit().beep();
}
}
});
Update:
You can change your class as follows:
public class EndCycleTextAreaRenderer extends JTextPane implements TableCellRenderer {
private final int maxNumberOfCharacters = 200;
public EndCycleTextAreaRenderer() {
setStyledDocument(new DefaultStyledDocument() {
#Override
public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
if ((getLength() + str.length()) <= maxNumberOfCharacters) {
super.insertString(offs, str, a);
} else {
Toolkit.getDefaultToolkit().beep();
}
}
});
}
}

Here is a sample program, for you where, as you enter the fourth time into the TextPane it will beep, without even you pressing the Enter key:
import javax.swing.*;
import javax.swing.text.*;
import java.awt.Toolkit;
public class TextPaneLimit extends JFrame
{
private JPanel panel;
private JTextPane tpane;
private AbstractDocument abDoc;
public TextPaneLimit()
{
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);
panel = new JPanel();
tpane = new JTextPane();
Document doc = tpane.getStyledDocument();
if (doc instanceof AbstractDocument)
{
abDoc = (AbstractDocument)doc;
abDoc.setDocumentFilter(new DocumentSizeFilter(3));
}
panel.add(tpane);
add(panel);
pack();
}
public static void main(String... args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
new TextPaneLimit().setVisible(true);
}
});
}
}
class DocumentSizeFilter extends DocumentFilter {
private int max_Characters;
private boolean DEBUG;
public DocumentSizeFilter(int max_Chars) {
max_Characters = max_Chars;
DEBUG = false;
}
public void insertString(FilterBypass fb
, int offset
, String str
, AttributeSet a)
throws BadLocationException {
if (DEBUG) {
System.out.println("In DocumentSizeFilter's insertString method");
}
if ((fb.getDocument().getLength() + str.length()) <= max_Characters)
super.insertString(fb, offset, str, a);
else
Toolkit.getDefaultToolkit().beep();
}
public void replace(FilterBypass fb
, int offset, int length
, String str, AttributeSet a)
throws BadLocationException {
if (DEBUG) {
System.out.println("In DocumentSizeFilter's replace method");
}
if ((fb.getDocument().getLength() + str.length()
- length) <= max_Characters)
super.replace(fb, offset, length, str, a);
else
Toolkit.getDefaultToolkit().beep();
}
}
Hope this might help.

I would suggest checking the # of characters with every key entered by adding a keyReleasedListener, it is something I used in a recent GUI of mine to check bounds seemingly instantly and display errors to the user as they typed.
Here is how I implemented it on one of my TextFields:
carbonTextField.addKeyListener(new java.awt.event.KeyAdapter()
{
public void keyReleased(java.awt.event.KeyEvent evt)
{
carbonTextFieldKeyReleased(evt);
}
});

Check the following code:
txtpnDesc.addKeyListener(new KeyAdapter() {
#Override
public void keyTyped(KeyEvent e) {
if(txtpnDesc.getText().length() == 30)
{
e.consume();
}
}
});