Java 中的乘法运算导致负值

Question

Why does the below calculation produce a negative value?

long interval = 0;

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

Answer 1

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;

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.

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);

Answer 2

Try this, it won't be negative:

long interval = 0;

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

Answer 3

Because the value of the equation is causing a number so big that it wraps around It will result in a Integer.Int

Answer 4

Your value is 2592000000 which is bigger than the maximum signed integer value 2^31 (2147483648). This is called integer overflow, the result overflows into negative.