Add one (new) Person to the list, keeping the list sorted.
String lastName = p.getLastName();
int i;
for (i=0; i<usrList.size(); i++)
if (lastName.compareTo(((Person)(usrList.get(i))).getLastName()) <= 0)
break;
usrList.add(i, p);
visList.add(p.getName(), i);
visList.select(i); // ensure current