JTextArea - only digit

Question

I need JTextArea, not JFormattedTextField, because I want 3 lines and on each lines one digits, how can I do it?

Answer 1

Extract the Document from the JTextArea, cast it to a PlainDocument and then add a DocumentFilter to the Document, filtering out all un-allowed input.

Please click this link for the Document Filter Tutorial.

For an example of the opposite, a DocumentFilter which prevents the user from typing numbers into the document, please see: Using DocumentFilter.FilterBypass. It would be easy to adapt this to your needs.