public boolean equals(Object o) {
if (this == o) return true;
else if (o == null || !o.getClass().equals(Pair.class)) return false;
else {
final Pair<Object, Object> that = (Pair<Object, Object>) o;
if (first != null ? !first.equals(that.first) : that.first != null) return false;
else return !(second != null ? !second.equals(that.second) : that.second != null);
}
}
