Jtextfield checking input

Question

hi all, i was wondering what may be the best way to check input. the current method i'm using is to handle the keyTyped event. for example i do not want to allow the user to enter letter "a":
         @Override
            public void keyTyped(java.awt.event.KeyEvent e) {
                if (e.getKeyChar()=='a') {
                    e.consume();
                }but the user can still copy and paste the letter into the text field. is there a proper way to check input which occurs into the TextField and acting on it ?

Answer 1

Pacerier wrote:
however if i'm right, not all documents have a document filter right?The reality of things is that all Document implementations shipped with the JRE extend AbstractDocument and can take DocumentFilters, so this is a non-issue. Further, Sun will never change the default Document type installed on the various text components, as that would break backwards compatibility.(1)
If you're super paranoid you can always ensure your Document takes a DocumentFilter like so:
JTextField field = new JTextField();
PlainDocument doc = new PlainDocument();
doc.setDocumentFilter(new MyDocumentFilter());
field.setDocument(doc);Most of the time people will just code defensively, like so:
Document doc = textComp.getDocument();
if (doc instanceof AbstractDocument) {
   AbstractDocument ad = (AbstractDocument)doc;
   // Do AbstractDocument-specific stuff
}knowing that the conditional should always be true.
(1) Technically they could, since JTextComponent only refers to its Document by interface, but the reality of it is that they won't, as too much code has been written around text components having PlainDocuments or DefaultStyledDocuments (whichever is appropriate), or at the very least AbstractDocuments.