英文:
Why does my variable resut in an overflow in Java?
问题
这是我的代码
num1 等是 int 变量
double numProduct1;
numProduct1 = (num1 * num2 * num3 * num4);
System.out.printf("%.3f ", numProduct1);
输入分别为 (num1,num2,num3,num4):
100000
200000
300000
500000
我的代码输出会是 -1679818752.000 而不是 3000000000000000000000.000。
英文:
Here is my code
num1 etc are int variable
double numProduct1;
numProduct1 = (num1 * num2 * num3 * num4);
System.out.printf("%.3f ", numProduct1);
Inputs are respectively (num1,num2,num3,num4):
100000
200000
300000
500000
my code would output -1679818752.000 instead of 3000000000000000000000.000
答案1
得分: 3
你以为将产品分配给 double 将允许您使用整个 double 范围，但事实并非如此。您只是将 结果 转换为 double。乘法仍然使用 int 进行，且适用于 int 范围。
本质上，这是乘法版本的 这个常见问题（嗯，不完全一样 :D）。
修复方法类似，只需使第一个操作数为 double（例如通过强制转换）：
numProduct1 = ((double)num1 * num2 * num3 * num4);
现在，表达式是一个 double 乘以一个 int，并且会发生 数值提升，将其他数字也提升为 double。
英文:
You thought that assigning the product to a double will allow you to use the whole range of double, but that isn't the case. You are only converting the result to double. The multiplication is still carried out with int, and the int range applies.
Essentially, this is the multiplication version of this common question (well, not exactly :D).
The fix is similar, simply make the first operand double (e.g. by casting):
numProduct1 = ((double)num1 * num2 * num3 * num4);
The expression is now a double multiplied by an int, and numeric promotion occurs, promoting the other numbers to double as well.
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