java - No blanks in JTextField

Question

How can I forbid users to put blanks into a JTextField?
It should not even be possible to write blanks.

Answer 1

I would suggest to set the Document of the JTextField with an extended PlainDocument in which you override the insertString method. (Also nice to limit the size...)
Something like:

Document doc = new PlainDocument() {
    @Override
    public void insertString(int offs, String str, AttributeSet attr)
    throws BadLocationException {
        String newstr = str.replaceAll(" ", "");  // could use "\s" instead of " "
        super.insertString(offs, newstr, attr);
    }

    @Override
    public void replace(int offs, int len, String str, AttributeSet attr) 
    throws BadLocationException {
        String newstr = str.replaceAll(" ", "");  // could use "\s" instead of " "
        super.replace(offs, len, newstr, attr);
    }
};
textField.setDocument(doc);

EDIT:
replace must also be overrided/implemented!