JAVA / MaskFormatter: Allow Placeholder Character

Question

I use the following code, to apply a MaskFormatter on my JFormattedTextField in order to make it accept IBANs (2 letters followed by 20 digits):

MaskFormatter formatter = new MaskFormatter("UU## #### #### #### #### ##");
formatter.setPlaceholderCharacter('_');
jFormattedTextField.setFormatterFactory(new DefaultFormatterFactory(formatter));

Whenever there's an empty space in that textfield, the placeholder character ('_') holds that place as intended. But once you focus a different textfield, the field will check if the String inside is valid, and reset it otherwise. However, I don't want it to change if it looks like this for example:

AA00 11_1 2222 ____ 4444 5555 66

In order to achieve that, I'd have to allow the placeholder character as a valid MaskCharacter in every position. Which would be achievable by copying the entire class and modifying isValidCharacter(), but that's dirty.

Is there a way to do something like?:

new MaskFormatter("[U^_][U^_][#^_][#^_] [#^_][#^_][#^_][#^_] [#^_][#^_][#^_][#^_] ...");

Or something like formatter.allowCharacter('_')

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It does sort of work with "**** **** **** **** **** **", but that doesn't force the user to input valid characters at the given positions, so it's not really what I'm looking for.

Answer 1

Method isValidCharacter() looks for below methods for validation. I guess, Setting appropriate values for in the below method would be more than enough

formatter.setValidCharacters("")
formatter.setInvalidCharacters("")