乘法-Java后的双值否定

Question

In my code i have following line.

double temp=(c12*fileSize);

• Here c12 is double and fileSizeis double
• c12 have a value 1700 and
• fileSize have a value 1944038

but after multiplication i am getting -990102696 .

Can any one help me on it? Is that some size limits went wrong?

Answer 1

(int)1700 * (int)1944038 is equal to your -990102696 .

Are you sure c12 and fileSize aren't integers? If they are, the multiplication occurs with integer types, integer overflow and it is being promoted to double afterwards .

Answer 2

Your c12 and fileSize are most likely ints (+1 Tomasz). Java multiplies the ints, which overflows, becoming negative, and then stores that negative value in your double. Cast c12 and fileSize to double before multiplying:

double c12 = 1700, fileSize = 1944038;
System.out.println(c12 * fileSize);

produces:

3.3048646E9

Answer 3

Hmm, I just tried that and I get "3.3048646E9". You shouldn't get any overflow wrap around on a double: if you exceed the maximum, it should turn into "Infinity".

I suspect the problem is in whatever you're trying to do to write this number. Or maybe you need to show us some more code.

Answer 4

Make a double on the fly:

double temp=(c12*1.0*fileSize);

else, an c12 as int will be multiplied by another int, and the result overflows, and is later - too late - converted to double.

c12 = 1700.0 
// or 
filesize = 1944038f 

would help, but a filesize as float/double looks fishy.

Answer 5

    double c12 = 1700;
    double fileSize = 1944038;
    double temp=(c12*fileSize);
    System.out.println(temp);

Gives 3.3048646E9

I bet your c12 and fileSize are ints.

Answer 6

使用BigDecimal乘法方法，这样可以在处理大型双数时防止潜在的过度问题 ：

BigDecimal temp = (new BigDecimal(fileSize)).multiply(new BigDecimal(c12));