英文:
Calculate product in Java, term vs. a 'for' loop, different results
问题
考虑：
long y = 1;
for (int i = 49; i > 43; i--) {
y*= i;
}
long x = 49*48*47*46*45*44; // = 1478412928
long y // = 10068347520
为什么结果不同，尽管计算方式都是偶数？
是否有解释？
英文:
Consider:
long y = 1;
for (int i = 49; i > 43; i--) {
y*= i;
}
long x = 49*48*47*46*45*44; // = 1478412928
long y // = 10068347520
Why are the results different although the calculation is even?
Is there an explanation?
答案1
得分: 4
49*48*47*46*45*44 是int文字的乘法，因此执行int乘法，导致int值。在将结果分配给long变量之前，在这种情况下会溢出（因为结果大于Integer.MAX_VALUE）。因此，结果是不正确的。
将其更改为 49L*48*47*46*45*44 或 (long)49*48*47*46*45*44 以执行long乘法。
另一方面，在你的第一次计算中，你从一个值为1的long变量开始，然后在每次迭代中将该long与一个int相乘，执行long乘法，因此没有溢出。
英文:
49*48*47*46*45*44 is a multiplication of int literals, and therefore performs int multiplications resulting in an int value. It overflows in this case (since the result is larger than Integer.MAX_VALUE) before you assign the result to the long variable. Hence the result is incorrect.
Change it to 49L*48*47*46*45*44 or (long)49*48*47*46*45*44 to perform long multiplication.
In your first calculation, on the other hand, you begin with a long variable whose value is 1, and the loop multiplies that long with an int in each iteration, performing long multiplication, so there's no overflow.
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