// in User.class; hasVoice() works perfectly fine
//...
public boolean hasVoice() {
return _prefix.indexOf('+') >= 0;
}
public boolean hasHalfop() {
  return _prefix.indexOf('%') >= 0;
}
//etc...

//in PircBot.java
//...
Hashtable users = (Hashtable) _channels.get(channel);
User newUser = null;
if (users != null) {
  Enumeration enumeration = users.elements();
  while(enumeration.hasMoreElements()) {
    User userObj = (User) enumeration.nextElement();
    if (userObj.getNick().equalsIgnoreCase(nick)) {
      if (userMode == OP_ADD) {
        if (userObj.hasVoice() && userObj.hasHalfop()) {
          newUser = new User("@%+", nick);
        }
        else if (userObj.hasVoice()) {
          newUser = new User("@+", nick);
        }
        else if (userObj.hasHalfop()) {
          newUser = new User("@%", nick);
        }
        else {
          newUser = new User("@", nick);
        }
      }
//etc...