JEdits must accept only numbers and dot sign

There are two JEdits edPrice and edPriceTill. If first JEdit is empty then second must be editable=false. I tried like this
--------------------------
DocumentListener priceDocListener = new DocumentListener() {
        public void changedUpdate(DocumentEvent e) {
            doCheck();
        }
        public void removeUpdate(DocumentEvent e) {
            doCheck();
        }
        public void insertUpdate(DocumentEvent e) {
            doCheck();
        }
        private void doCheck() {
// HERE I  NEED TO INSERT IT
//            e.getChange(elem);
            if(price.getText().length()<=0) {
                priceTill.setEditable(false);
                priceTill.setText("");
            } else {
                priceTill.setEditable(true);
            }
        }
    };
--------------------------
Now I need to allow this edit to recieve only numbers and '.'. It seems to be done using
e.getChange(elem);
but it requires `elem` as parameter, where can i get it? Or am i wrong.