Limiting the number of characters in a JTextField

Question

I want to set the maximum length of a JTextField  so that you can t enter more characters than the limit  This is the code I have so far         textField   new JTextField        textField setBounds 40  39  105  20       contentPane add textField       textField setColumns 10     Is there any simple way to put a limit on the number of characters

User · Answer

private  void validateInput                    if  filenametextfield getText   length    lt   3                        errorMsg2 setForeground Color RED                      else if filenametextfield getText   length    gt   3  amp  amp  filenametextfield getText   length   lt   25                          errorMsg2 setForeground frame getBackground                  errorMsg setForeground frame2 getBackground                         else if filenametextfield getText   length    gt   25                          remove errorMsg2                errorMsg setForeground Color RED                filenametextfield addKeyListener new KeyAdapter                       public void keyTyped KeyEvent e                         if filenametextfield getText   length   gt  25                                                     e consume                             e getModifiers

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Here is an optimized version of npinti s answer   import javax swing text AttributeSet  import javax swing text BadLocationException  import javax swing text JTextComponent  import javax swing text PlainDocument  import java awt     public class TextComponentLimit extends PlainDocument       private int charactersLimit       private TextComponentLimit int charactersLimit                this charactersLimit   charactersLimit              Override     public void insertString int offset  String input  AttributeSet attributeSet  throws BadLocationException               if  isAllowed input                         super insertString offset  input  attributeSet             else                       Toolkit getDefaultToolkit   beep                         private boolean isAllowed String string                return  getLength     string length     lt   charactersLimit             public static void addTo JTextComponent textComponent  int charactersLimit                TextComponentLimit textFieldLimit   new TextComponentLimit charactersLimit           textComponent setDocument textFieldLimit             To add a limit to your JTextComponent  simply write the following line of code   JTextFieldLimit addTo myTextField  myMaximumLength

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x000D   x000D  private void jTextField1KeyTyped java awt event KeyEvent evt                                       x000D  if  jTextField1 getText   length   gt  3    x000D              getToolkit   beep    x000D              evt consume    x000D            x000D        x000D   x000D   x000D

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private void jTextField1KeyPressed java awt event KeyEvent evt        if jTextField1 getText   length   gt  5                jTextField1 setText jTextField1 getText   substring 0  4              I have taken a jtextfield whose name is jTextField1  the code is in its key pressed event  I Have tested it and it works  And  I am using the NetBeans IDE

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Since the introduction of the DocumentFilter in Java 1 4  the need to override  Document has been lessoned   DocumentFilter provides the means for filtering content been passed to the Document before it actually reaches it   These allows the field to continue to maintain what ever document it needs  while providing the means to filter the input from the user   import java awt EventQueue  import java awt GridBagLayout  import javax swing JFrame  import javax swing JPasswordField  import javax swing JTextField  import javax swing UIManager  import javax swing UnsupportedLookAndFeelException  import javax swing text AbstractDocument  import javax swing text AttributeSet  import javax swing text BadLocationException  import javax swing text DocumentFilter   public class LimitTextField        public static void main String   args            new LimitTextField               public LimitTextField             EventQueue invokeLater new Runnable                  Override             public void run                     try                       UIManager setLookAndFeel UIManager getSystemLookAndFeelClassName                       catch  ClassNotFoundException   InstantiationException   IllegalAccessException   UnsupportedLookAndFeelException ex                        ex printStackTrace                                       JTextField pfPassword   new JTextField 20                     AbstractDocument pfPassword getDocument    setDocumentFilter new LimitDocumentFilter 15                     JFrame frame   new JFrame  Testing                    frame setDefaultCloseOperation JFrame EXIT ON CLOSE                   frame setLayout new GridBagLayout                     frame add pfPassword                   frame pack                    frame setLocationRelativeTo null                   frame setVisible true                                        public class LimitDocumentFilter extends DocumentFilter            private int limit           public LimitDocumentFilter int limit                if  limit  lt   0                    throw new IllegalArgumentException  Limit can not be  lt   0                              this limit   limit                      Override         public void replace FilterBypass fb  int offset  int length  String text  AttributeSet attrs  throws BadLocationException               int currentLength   fb getDocument   getLength                int overLimit    currentLength   text length    - limit - length              if  overLimit  gt  0                    text   text substring 0  text length   - overLimit                             if  text length    gt  0                    super replace fb  offset  length  text  attrs

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public void Letters JTextField a        a addKeyListener new KeyAdapter              Override         public void keyTyped java awt event KeyEvent e                char c   e getKeyChar                if  Character isDigit c                     e consume                              if  Character isLetter c                     e setKeyChar Character toUpperCase c                                       public void Numbers JTextField a        a addKeyListener new KeyAdapter              Override         public void keyTyped java awt event KeyEvent e                char c   e getKeyChar                if   Character isDigit c                     e consume                                       public void Caracters final JTextField a  final int lim        a addKeyListener new KeyAdapter              Override         public void keyTyped java awt event KeyEvent ke                if  a getText   length      lim                    ke consume

User · Answer

It s weird that the Swing toolkit doesn t include this functionality  but here s the best answer to your question       textField   new JTextField        textField addKeyListener new KeyAdapter              Override         public void keyTyped KeyEvent e                if  txtGuess getText   length    gt   3      limit to 3 characters                 e consume                        I use this in a fun guessing game example in my Udemy com course  Learn Java Like a Kid    Cheers - Bryson

User · Answer

You can do something like this  taken from here    import java awt FlowLayout   import javax swing JFrame  import javax swing JLabel  import javax swing JTextField  import javax swing text AttributeSet  import javax swing text BadLocationException  import javax swing text PlainDocument   class JTextFieldLimit extends PlainDocument     private int limit    JTextFieldLimit int limit        super        this limit   limit         JTextFieldLimit int limit  boolean upper        super        this limit   limit         public void insertString int offset  String str  AttributeSet attr  throws BadLocationException       if  str    null        return       if   getLength     str length     lt   limit          super insertString offset  str  attr                public class Main extends JFrame     JTextField textfield1     JLabel label1     public void init         setLayout new FlowLayout         label1   new JLabel  max 10 chars        textfield1   new JTextField 15       add label1       add textfield1       textfield1 setDocument new JTextFieldLimit 10         setSize 300 300       setVisible true           Edit  Take a look at this previous SO post  You could intercept key press events and add ignore them according to the current amount of characters in the textfield

[java] Limiting the number of characters in a JTextField

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