How to create TextField that only accept letter (Java)

If you use a normal JTextField then all character(s) can be accepted. But sometimes we need a textfield that only accept letter ('a'-'z' and 'A'-'Z').
I Hope this JLetterField.java can solve your problem.

import javax.swing.JTextField;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.PlainDocument;

public class JLetterField
extends JTextField
{
    public JLetterField(int cols) {
        super("",cols);
    }

    protected Document createDefaultModel() {
        return new LetterDocument();
    }
    
    class LetterDocument extends PlainDocument {
        public void insertString(int offs,String str,AttributeSet a)
        throws BadLocationException
        {
            if(str==null) return;
            char [] before = str.toCharArray();
            String after = "";
            for(int i=0;i < before.length;i++)
            {
                if( (before[i]>='a' && before[i]<='z') || (before[i]>='A' && before[i]<='Z') )
                    after += before[i];
            }
            super.insertString(offs,after,a);
        }
    }    
}