JAVA中的日期比较问题

Question

JAVA中的日期用Date.before()和Date.after(),还是直接Date.getTime比较,哪个好?

Answer 1

根据 OpenJDK 7 的源代码：

public boolean before(Date when) {
    return getMillisOf(this) < getMillisOf(when);
}

public boolean after(Date when) {
    return getMillisOf(this) > getMillisOf(when);
}

public long getTime() {
    return getTimeImpl();
}

private final long getTimeImpl() {
    if (cdate != null && !cdate.isNormalized()) {
        normalize();
    }
    return fastTime;
}

static final long getMillisOf(Date date) {
    if (date.cdate == null || date.cdate.isNormalized()) {
        return date.fastTime;
    }
    BaseCalendar.Date d = (BaseCalendar.Date) date.cdate.clone();
    return gcal.getTime(d);
}

private final BaseCalendar.Date normalize() {
    if (cdate == null) {
        BaseCalendar cal = getCalendarSystem(fastTime);
        cdate = (BaseCalendar.Date) cal.getCalendarDate(fastTime, TimeZone.getDefaultRef());
        return cdate;
    }
    if (!cdate.isNormalized()) {
        cdate = normalize(cdate);
    }
    TimeZone tz = TimeZone.getDefaultRef();
    if (tz != cdate.getZone()) {
        cdate.setZone(tz);
        CalendarSystem cal = getCalendarSystem(cdate);
        cal.getCalendarDate(fastTime, cdate);
    }
    return cdate;
}

看起来 before 和　after　会稍微快一点点。不过也有的 Java 实现里面 before 和 after 就是调用 getTime() 的。