public int compareTo(Object o) { if (this == o)
public int compareTo(MailItem that) { if (this == that)
    public int compareTo(Object o) {        if (this == o)            return 0;        MailItem that = (MailItem) o;        long myDate = getChangeDate(), theirDate = that.getChangeDate();        return (myDate < theirDate ? -1 : (myDate == theirDate ? 0 : 1));    }