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I want to limit the number of characters to be inserted in a JTextField to 10 character. I use a graphical interface under netbeans.thanks.

camickr
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ala
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  • add a `documentListener` to you `JTextField` – Blip May 04 '15 at 10:18
  • This question was originally closed as a duplicate to this question: http://stackoverflow.com/questions/3519151/how-to-limit-the-number-of-characters-in-jtextfield. That is an old answer. The Swing API has evolved and the more current solution would be to use a DocumentFilter, so I re opened the question. – camickr May 04 '15 at 13:49

3 Answers3

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To prevent the user from entering more the 10 charaters in a textfield you can use a document.

Create a simple document by extending PlainDocument and to change the behavior override 

public void insertString(...) throws BadLocationException

This is an example

public class MaxLengthTextDocument extends PlainDocument {
    //Store maximum characters permitted
    private int maxChars;

    @Override
    public void insertString(int offs, String str, AttributeSet a)
            throws BadLocationException {
        // the length of string that will be created is getLength() + str.length()
        if(str != null && (getLength() + str.length() < maxChars)){
            super.insertString(offs, str, a);
        }
    }

}

After this, only insert your implementation in JTextField, this way:

...
MaxLengthTextDocument maxLength = new MaxLengthTextDocument();
maxLength.setMaxChars(10); 

jTextField.setDocument(maxLength);
...

And that's it!

MChaker
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  • Quick post, I know this is old but `(getLength() + str.length() < maxChars))` should really be `(getLength() + str.length() <= maxChars))` otherwise one less character than what is set will be allowed into the text field. Thanks for the post though, just helped me out! – Swemoph Oct 09 '16 at 01:44
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Best thing is you will get running demo ;)

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()) <= limit) {
      super.insertString(offset, str, attr);
    }
  }
}

public class Main extends JFrame {
  JTextField textfield1;

  JLabel label1;

  public static void main(String[]args){
      new Main().init();
  }
  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);
  }
}
Sarz
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0

Read the section from the Swing tutorial on Implementing a DocumentFilter for a more current solution.

This solution will work an any Document, not just a PlainDocument.

camickr
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