new Date(new Date().getTime()-25 * 24 * 60 * 60 * 1000)获得了意外日期 [英] new Date(new Date().getTime()-25 * 24 * 60 * 60 * 1000) got unexpected date

问题描述

我想生成日期列表，但发现日期从-25 * 24 * 60 * 60 * 1000开始错误

I would like to generate a list of dates, but found out the date is wrong start from - 25 * 24 * 60 * 60 * 1000

我的本​​地日期是2016年7月17日.我

My local date is 2016-07-17. I got

2016-07-17
2016-07-16
2016-07-15
...
2016-06-23
2016-08-11

我不知道 2016-08-11 的来源.我将25分解为24和-1，如下所示( xxx 和 yyy )，然后我得到了正确的日期 2016-06-22 .

I have no idea where the 2016-08-11 comes from. I broke down the 25 to 24 and -1 as below (xxx and yyy), and then I got the correct date 2016-06-22.

为什么 xxx 可以工作，但是 yyy 不能?

Why does xxx work but yyy Doesn't?

Date xxx = new Date(new Date().getTime()-24 * 24 * 60 * 60 * 1000 -1 * 24 * 60 * 60 * 1000);
Date yyy = new Date(new Date().getTime()-25 * 24 * 60 * 60 * 1000);

这是我的代码:从i = 25起日期是错误的

Here is my code: date is wrong from i=25

for (int i=0; i<240;i++) {
    Date dt = new Date(new Date().getTime() - i * 24 * 60 * 60 * 1000);
    Log.e(TAG,Global.sdfDateTime19.format(dt));
}

推荐答案

您正在溢出 int 的范围. i * 24 * 60 * 60 * 1000 产生一个 int (然后从 getDate 的 long 中减去它)).

You're overflowing the range of int. i * 24 * 60 * 60 * 1000 yields an int (which is then subtracted from the long from getDate).

当 i 为24时没关系，因为结果为2,073,600,000，小于 int 的最大正值2,147,483,647.但是当达到 i = 25 时，就会回绕(如果不限制为 int ，则该值为21.6亿，这太大了.)

It's okay when i is 24, because the result is 2,073,600,000, which is less than the maximum positive value for an int, 2,147,483,647. But when you reach i = 25, you wrap around (the value if you weren't constrained to int would be 2,160,000,000, which is too big).

只要将 i 声明为long或将24设置为 long ，即可将其设置为 long 乘以:

Just make it a long multiplication, either by declaring i as a long or by making the 24 a long:

Date dt = new Date(new Date().getTime() - i * 24L * 60 * 60 * 1000);
// ---------------------------------------------^

为什么xxx有效，但yyy不起作用?

Why xxx works but yyy not work?

因为您已将乘法分解为两部分(为了清楚起见，我在其中添加了一个空格，因为 -1 否则看起来像是负数而不是减法运算符，后跟 1 ):

Because you've broken up the multiplication into two parts (I've added a space in there for clarity, since the -1 otherwise looks like a negative number rather than the subtraction operator followed by 1):

Date xxx = new Date(new Date().getTime()-24 * 24 * 60 * 60 * 1000 - 1 * 24 * 60 * 60 * 1000);
// The first part -----------------------^^^^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^^^^
// The second part ------------------------------------------------/

...，并且您将其拆分成两个部分的任何一个都不会溢出 int 的范围.

... and neither of the two parts you've broken it up into overflows the range of int.

通常，我不建议您以这种方式操作日期，尤其是因为并非所有的日期都恰好有24小时(考虑进入和退出夏令时的日期).我将使用一个库来让您在工作日"级别上工作，例如Java 8 java.time 或JodaTime或类似的库.

In general, I wouldn't suggest manipulating dates this way, not least because not all days have exactly 24 hours in them (consider the days going into and out of daylight saving time). I'd use a library that lets you work at the "day" level, such as the Java 8 java.time stuff, or JodaTime, or similar.

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