How to use JFormattedTextField allowing only letters and numbers

Question

I have this code and cannot get MaskFormatter right
maskformatter

MaskFormatter formatter = null;
  try {
    formatter = new MaskFormatter("HHHHHHH");
  } catch (ParseException e) {
    e.printStackTrace();
  }

txtTroll = new JFormattedTextField(formatter);

I need Any hex character (0-9, a-z or A-Z) and the "H" should
give me only (0-9, a-z or A-Z) but im getting it wrong.

When i type text only capital letters are typed and it's slow to
and when i click away from the txtTroll all letters vanish

Answer 1

u can use another solution that i prefer

write ur Document class and rewrite it's insertString method using regex expr

example:

import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.text.AttributeSet;
import javax.swing.text.PlainDocument;

/**
*
* @author cpp-qt
*/
public class HexDocument extends PlainDocument {

private String text = "";

@Override
public void insertString(int offset, String txt, AttributeSet a) {
    try {
        text = getText(0, getLength());
        if ((text + txt).matches("[0-9a-fA-F]{0,7}")) {
            super.insertString(offset, txt, a);
        }
     } catch (Exception ex) {
        Logger.getLogger(HexDocument.class.getName()).log(Level.SEVERE, null, ex);
     }

    }
}

then

set it as ur textField's document like this this.jTextField1.setDocument(new HexDocument());

i think this is better than using jFormattedTextField