NumberFormat parse not strict enough

Question

I have a JFormattedTextField with a NumberFormat with Locale.US. So the decimal separator is the point and the grouping separator is the comma.

Now I type the string "1,23" in this text field and move the focus to another component. I would expect the string to disappear (like it does when i type "a" instead of "1,23") because it is obviously not a valid representation of a number when using Locale.US. But instead the text in the text field is changed to "123".

This is because the used NumberFormat is not strict when parsing and simply ignores the comma.

Question: How can I tell NumberFormat to throw a ParseException in this case so the text field will be empty after moving the focus to another component?

Test Code:

JDialog dialog = new JDialog();
JPanel panel = new JPanel(new BorderLayout());
dialog.getContentPane().add(panel);

NumberFormat nf = NumberFormat.getInstance(Locale.US);
JFormattedTextField textField = new JFormattedTextField(nf);
textField.setText("1,23");
panel.add(textField, BorderLayout.CENTER);
panel.add(new JButton("focus"), BorderLayout.EAST);

dialog.pack();
dialog.setVisible(true);

Move the focus from the text field to the button and the text will change to "123".

Answer 1

I would suggest you to use regex and use the match fucntion like this:

matches("\\d+([.,])?")

Also if you will use Integer.parseInt(String) will throw an exception if it will be parsed or you can use Double.parseDouble(value)