Only A-Z letters

Question

hi, i've got class:
class UpperCaseField extends JTextField {
     public UpperCaseField(int cols) {
         super(cols);
     protected Document createDefaultModel() {
         return new UpperCaseDocument();
     static class UpperCaseDocument extends PlainDocument {
         public void insertString(int offs, String str, AttributeSet a)
             throws BadLocationException {
             if (str == null) {
                 return;
             char[] upper = str.toCharArray();
             for (int i = 0; i < upper.length; i++) {
                 upper[i] = Character.toUpperCase(upper);
super.insertString(offs, new String(upper), a);
i took it from help file.
But i want add something else: i want to do that user can to type only letters from range A-Z (without digits, special signs for examlpe "/,. '...");
how can i do that?
thud
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Answer 1

ok, i add that method to my class:
    protected MaskFormatter createFormatter(String s) {
        MaskFormatter formatter = null;
        try {
            formatter = new MaskFormatter(s);
        } catch (java.text.ParseException exc) {
            System.err.println("formatter is bad: " + exc.getMessage());
            System.exit(-1);
        return formatter;
    }and then:
        JFormattedText Field keyField = new JFormattedTextField(createFormatter("UUUUU"));
        keyField.setColumns(27);and it works well :), but...
the numbers of "UUUUU" means how many letters could user type. But i want that the user could type 1024 characters, so how can i do that??
I don't wanna write "UUUUUUUUUUUUU..."-1024-times :/; Is there another way to do this??
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