Java中的浮点计算错误

Question

Help, I got a problem when adding double value with negative number
A sample program to show the problem:

    double newX = 850.0;
    double delta = -1.6994427191177073E12;
    double total = delta + newX;
    System.out.println("newX:" + newX);
    System.out.println("delta:" + delta);
    System.out.println("total:" + total);

but the given output is:

 newX:850.0
 delta:-1.6994427191177073E12
 total:-1.6994427182677073E12

I would expect the total value to be around "848.30055729". How to handle this calculation?

Regards,

Dennis

Answer 1

The computation is correct.

Lets start by converting your number from scientific notation

-1.6994427191177073E12

to decimal fixed-point notation:

-1699442719117.7073

This is because E12 means that the number to the left of E is multiplied by 10 ¹² .

Once you perform the addition of that number and 850.0 , you get the result

-1699442718267.7073

Once you convert it to scientific notation by bringing the decimal point all the way to the left, you get the result printed by your program.