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Set Maxlength for JTextField??

Posted on 2004-03-22
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1,805 Views
Last Modified: 2012-06-27
is there any way to set the maxlenth of the Jtextfield ?? restricted to 10 char
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Question by:M_I2
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27 Comments
 
LVL 14

Expert Comment

by:StillUnAware
ID: 10655740
//something like that :)

import javax.swing.*;
import javax.swing.text.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.event.*;

public class DocumentUse extends JFrame {
  DocumentUse() {
    Container cp = getContentPane();
    final JTextField tf = new JTextField();
    tf.getDocument().addDocumentListener(new DocumentListener() {
      public void changedUpdate(DocumentEvent e) {
        if(tf.getText().length() > 10)
          tf.setText(tf.getText().substring(10));
      }
      public void insertUpdate(DocumentEvent e) {
        if(tf.getText().length() > 10)
          tf.setText(tf.getText().substring(10));
      }
      public void removeUpdate(DocumentEvent e) {
        if(tf.getText().length() > 10)
          tf.setText(tf.getText().substring(10));
      }
    });
    cp.add(tf);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    pack();
    setVisible(true);
  }
  public static void main(String[] args) {
    DocumentUse du = new DocumentUse();
  }
}
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LVL 16

Expert Comment

by:krakatoa
ID: 10656104
Can't get the above code to work.

Another way would be:

int MaxLen;
String mTF;
mTF = myTextField.getText().length()>MaxLen?myTextField.getText().substring(0,MaxLen):myTextField.getText();

myTextField.setText(mTF);
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LVL 86

Assisted Solution

by:CEHJ
CEHJ earned 50 total points
ID: 10656357
This is a case that would be better using a custom document than a document listener. see http://oldlook.experts-exchange.com:8080/Programming/Programming_Languages/Java/Q_20747816.html
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LVL 37

Accepted Solution

by:
zzynx earned 75 total points
ID: 10656419
I made a working one. Just test it.

import javax.swing.*;
import javax.swing.text.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.event.*;

public class DocumentUse extends JFrame {
   
    public class MyDocument extends PlainDocument {
   
        private int maxAllowedChars = 0;

        public MyDocument(int maxAllowed) {
            super();
            maxAllowedChars = maxAllowed;
        }

        public void insertString(int index, String s, AttributeSet a)
                                            throws BadLocationException {
             if (s == null || s.length() == 0)
                 return;
             StringBuffer t = new StringBuffer(getLength() + s.length());
             t.append(getText(0, index));
             t.append(s);
             t.append(getText(index, getLength() - index));
             if (t.length()>maxAllowedChars) return; // don't allow more than x chars
             super.insertString(index, s, a);
        }
    }    
   
    public class MyField extends JTextField {
        public MyField(int width) { super(width); }
        public MyField() { super(); }
        protected Document createDefaultModel() {
            return new MyDocument(10);
        }
    }
   
    public DocumentUse() {
        Container cp = getContentPane();
        final MyField tf = new MyField();

        cp.add(tf);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pack();
        setVisible(true);
    }
 
  public static void main(String[] args) {
    DocumentUse du = new DocumentUse();
  }
}
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LVL 86

Expert Comment

by:CEHJ
ID: 10656432
...but i just posted a (link to a) working one...?
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LVL 37

Expert Comment

by:zzynx
ID: 10656446
Sorry CEHJ, I didn't refresh before I posted.
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LVL 86

Expert Comment

by:CEHJ
ID: 10656458
No problem
0
 
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Expert Comment

by:twobitadder
ID: 10660895
doesn't
 textField.setColumns(10);
do this?
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LVL 16

Expert Comment

by:krakatoa
ID: 10661270
>> do this?

Lol, that's what I was thinking and have never tried it!! But, yeh, it should - shouldn't it?
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LVL 37

Expert Comment

by:zzynx
ID: 10665181
>> it should - shouldn't it?
LOL also

Why don't you try it?
In my example replace

        final MyField tf = new MyField();

by

        final JTextField tf = new JTextField();
        tf.setColumns(10);

P.S. If you don't want to try it yourself, here's the result: it doesn't work that way.
;-)
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LVL 86

Expert Comment

by:CEHJ
ID: 10666743
>>here's the result: it doesn't work that way.

Too late - i could have saved you both the bother ;-) Must be worth a few points in a split for the person who explains this conundrum...
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Expert Comment

by:zzynx
ID: 10667155
I don't understand what you mean to say CEHJ.

Hey M_I2, still alive?
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Expert Comment

by:CEHJ
ID: 10667344
>>I don't understand what you mean to say CEHJ.

By my first, or my second sentence?
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Expert Comment

by:zzynx
ID: 10668002
Both
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by:CEHJ
ID: 10668111
>>Too late - i could have saved you both the bother

Meant that everyone was asking if tf.setColumns(10); or similar would work - it doesn't - and had i got there in time i could have told everyone

>>Must be worth a few points in a split for the person who explains this conundrum...

Means that i have never taken the time and trouble to discover *why* this doesn't work and i'm encouraging someone to find out and also encouraging M_I2 to give the discoverer some points in a split.

All clear?
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Expert Comment

by:zzynx
ID: 10668216
>> All clear?
Yeah. Thanks for explaining.

>> Means that i have never taken the time and trouble to discover *why* this doesn't work
Why should it. It has nothing to do with the number of characters you can input.

The comment in the constructor
            public JTextField(int columns)
says

     * @param columns  the number of columns to use to calculate
     *   the preferred width; if columns is set to zero, the
     *   preferred width will be whatever naturally results from
     *   the component implementation

the java help for
           SetColumn()
says:
Sets the number of columns in this text field. A column is an approximate average character width that is platform-dependent.

So, its all about width, not about # of characters allowed to input.
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Expert Comment

by:zzynx
ID: 10668244
>> and also encouraging M_I2 to give the discoverer some points in a split.
If M_I2 is still alive ;)
I'm willing to accept them ;)
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Expert Comment

by:krakatoa
ID: 10668261
setColumns() just sets the display width, but you can type as much in as you like. How about that?
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by:CEHJ
ID: 10668268
Thanks for saving me the trouble ;-)
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Expert Comment

by:zzynx
ID: 10668392
>> setColumns() just sets the display width, but you can type as much in as you like.
>> How about that?
Too late ;)

>> Thanks for saving me the trouble ;-)
You're welcome
;)
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Expert Comment

by:krakatoa
ID: 10668443
>> Too late ;)
 ?

Where's that been said explicitly before? Remember, the question is for the benefit of the questioner, not the experts' fraternity.
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LVL 37

Expert Comment

by:zzynx
ID: 10668581
>>Where's that been said explicitly before?
In one of my previous comments:
      >> So, its all about width, not about # of characters allowed to input.
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LVL 16

Expert Comment

by:krakatoa
ID: 10668610
ok, point taken. I'll blame it on EE's oldlook posting bug earlier.
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Author Comment

by:M_I2
ID: 10697811
Sorry for late reply ;) but i was away past few days......

i would try out these code now.
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Author Comment

by:M_I2
ID: 10697838
i think that really works....but need some time to digest these codes

>> Hey M_I2, still alive?
and also actually i am alive!! but not available at all times

Well that's about it thanks for all your all for helping ;)
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Expert Comment

by:CEHJ
ID: 10697946
8-)
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Expert Comment

by:zzynx
ID: 10701958
Thanks for accepting.
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