1000 * 60 * 60 * 24 * 30就产生负号 [英] 1000 * 60 * 60 * 24 * 30 results in a negative number

问题描述

我试图来计算30天乘以毫秒然而，结果不断地最终被一个负数days_30的价值，我不知道为什么。

I'm attempting to calculate 30 days by multiplying milliseconds however the result continually ends up being a negative number for the value of days_30 and I'm not sure why.

任何建议都大大AP preciated！

Any suggestions are greatly appreciated!

code片断：

// check to ensure proper time has elapsed
                SharedPreferences pref = getApplicationContext()
                        .getSharedPreferences("DataCountService", 0);
                 long days_30 = 1000 * 60 * 60 * 24 * 30;
                 long oldTime = pref.getLong("smstimestamp", 0);
                long newTime = System.currentTimeMillis();
                 if(newTime - oldTime >= days_30){

在days_30值结果：-1702967296

days_30 value results in: -1702967296

P.S。

 double days_30 = 1000 * 60 * 60 * 24 * 30;
                 double oldTime = pref.getLong("smstimestamp", 0);
                double newTime = System.currentTimeMillis();
                 if(newTime - oldTime >= days_30){

结果在一个较小的 - 但仍然负数。 -1.702967296E9

Results in a smaller - but still negative number. -1.702967296E9

推荐答案

您成倍整数在一起，溢出发生的原因的最大整数 2 ^ 31 - 1 。只有乘法后，它会转换到长。先拿号作为长。

You are multiplying ints together, and overflow occurs because the maximum integer is 2^31 - 1. Only after the multiplications does it get converted to a long. Cast the first number as a long.

long days_30 = (long) 1000 * 60 * 60 * 24 * 30;

或使用长的文字：

long days_30 = 1000L * 60 * 60 * 24 * 30;

这将迫使长的数学运算，从一开始。

That will force long math operations from the start.

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