BigInteger returning negative numbers [duplicate]

问题

This question already has answers here:

Why do these two multiplication operations give different results? (2 answers)

Closed 5 years ago.

why this math return negative numbers for some numbers:

int x = 351;

    String bigValue= ((50*x*x*x-150*x*x+400*x)/3) + "";
    BigInteger resultInteger = new BigInteger(bigValue);
    System.out.println(resultInteger);

result -> 714612600

but if i use 352

result -> -710900565

for x=500 -> 639244234

WHY?

回答1:

This line here:

(50*x*x*x-150*x*x+400*x)/3

Is using integers, which can overflow. If an integer hits the max (2^31-1), it will overflow to -2^31.

You need to use BigIntegers here, something like this:

Biginteger bx = new BigInteger(x);
BigInteger new BigInteger(50).multiply(bx.pow(3)).multiply(new BigInteger(-150))
    .multiply(bx.pow(2)).multiply(new BigInteger(400)).multiply(bx).divide(3);

来源：https://stackoverflow.com/questions/24223440/biginteger-returning-negative-numbers