java 7 比较两个date是不是同一天 相差几天

可以使用Java 7中的Calendar类来比较两个Date是否为同一天，以及计算它们之间相差的天数。

比较两个Date是否为同一天：

public static boolean isSameDay(Date date1, Date date2) {
    Calendar cal1 = Calendar.getInstance();
    cal1.setTime(date1);
    Calendar cal2 = Calendar.getInstance();
    cal2.setTime(date2);
    return cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR)
            && cal1.get(Calendar.MONTH) == cal2.get(Calendar.MONTH)
            && cal1.get(Calendar.DAY_OF_MONTH) == cal2.get(Calendar.DAY_OF_MONTH);
}

计算两个Date之间相差的天数：

public static int daysBetween(Date date1, Date date2) {
    Calendar cal1 = Calendar.getInstance();
    cal1.setTime(date1);
    Calendar cal2 = Calendar.getInstance();
    cal2.setTime(date2);
    cal1.set(Calendar.HOUR_OF_DAY, 0);
    cal1.set(Calendar.MINUTE, 0);
    cal1.set(Calendar.SECOND, 0);
    cal1.set(Calendar.MILLISECOND, 0);
    cal2.set(Calendar.HOUR_OF_DAY, 0);
    cal2.set(Calendar.MINUTE, 0);
    cal2.set(Calendar.SECOND, 0);
    cal2.set(Calendar.MILLISECOND, 0);
    long diff = cal2.getTimeInMillis() - cal1.getTimeInMillis();
    return (int) (diff / (24 * 60 * 60 * 1000));
}

注意，在计算相差天数时，需要将两个Date的时间部分设置为0，以确保只计算日期的差异。