为什么我的变量会导致 Java 溢出？

Question

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

Answer 1

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 (eg 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.