How in Java I can create a field that can accept only digits and once dot?

I look all over the net and all the things I tried didn't work....

I found that I can use some JTextFormatterField but it didn't work.

Then I found that I can use DocumentFilter with regex and that what I did:

JTextField jFormattedTextFieldMoneyToConvert = new JTextField();
    ((AbstractDocument) jFormattedTextFieldMoneyToConvert.getDocument()).setDocumentFilter(new DocumentFilter(){
        Pattern regEx = Pattern.compile("^\\d+\\.?\\d*$");

        @Override
        public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
            Matcher matcher = regEx.matcher(text);
            if (!matcher.matches()) {
                return;
            }
            super.replace(fb, offset, length, text, attrs);
        }
    });

but it doesn't work...It accepts only digits. I want it to accept also dots. And I also need it to not to start with a dot and not to end with a dot.

what I'm doing wrong?

Copyright Notice：Content Author:「Alex K」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/30167524/how-in-java-i-can-create-a-field-that-can-accept-only-digits-and-once-dot