Java中的乘法运算导致负值 [英] Multiplication operation in Java is resulting in negative value

问题描述

为什么以下计算产生负值？

Why does the below calculation produce a negative value?

long interval = 0;

interval = ((60000 * 60) * 24) * 30;

推荐答案

正在评估其中的每个表达式（在编译时）时间，当然;它是一个常数），因为 int * int 而不是 long * long 。结果在某些时候溢出。所以只需使用 L 使所有操作数文字变长：

Every expression in there is being evaluated (at compile-time, of course; it's a constant) as int * int instead of long * long. The result overflows at some point. So just use L to make all the operand literals long:

interval = ((60000L * 60L) * 24L) * 30L;

当然，只有使一些的操作数长，你才能逃脱，但我倾向于发现更改一切更容易。

Of course you could get away with only making some of the operands longs, but I tend to find it's easier to just change everything.

说完所有这些，如果你正在寻找30天毫秒，它会最好使用：

Having said all of this, if you're looking for "30 days-worth of milliseconds" it would be better to use:

long interval = TimeUnit.DAYS.toMillis(30);

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