Java Double变量有奇怪的值 [英] Java Double variables have strange values

问题描述

可能重复：

浮点运算不能在Java中产生精确的结果

我正在做这个简单的划分，但我得到一个非常奇怪的输出：

  double a = 60 / （1.2-1.1）; 
  

a => 600.0000000000008

当它应该是600。

提前感谢

解决方案

754二进制双，我们需要以二进制表示方式考虑1.1和1.2：

  1.2 = 0b1.001100110011001100110011001100110011001100110011001100110011 ... 
 1.1 = 0b1.000110011001100110011001100110011001100110011001100110011001 ... 
  

请注意，我们需要无限多的位来准确地表示它们在二进制。双重只有53位的意义，我们必须把数字切断：

  1.2 = 0b1.001100110011001100110011001100110011001100110011001100110011 ... 
 1.1 = 0b1.000110011001100110011001100110011001100110011001100110011001 ... 
 ^ round from here 
 ==> 
 1.2〜0b1.0011001100110011001100110011001100110011001100110011 
（=恰好1.1999999999999999555910790149937383830547332763671875）
 1.1〜0b1.0001100110011001100110011001100110011001100110011010 
（=恰好1.100000000000000088817841970012523233890533447265625）
  
  1.2〜0b1.0011001100110011001100110011001100110011001100110011 
  -  1.1〜0b1.0001100110011001100110011001100110011001100110011010 
 ------------------------------------ ---------------------------- 
 0b0.00011001100110011001100110011001100110011001100110010000 
（=正好是0.09999999999999986677323704498121514916419982910156250000）
  
我们实际上可以计算出60 / 0.09999999999998667732370449812151491641998291015625，这给了s 
  600.0000000000007993605777301137740672368493927467455286920109359612256820927 ... 
 ^第16个有效数字
  
匹配OP的结果
  600.0000000000008 
  
 

  
Possible Duplicate:

  Floating point arithmetic not producing exact results in Java
I was doing this simple division but I get a very strange output:
double a = 60/(1.2-1.1);
a => 600.0000000000008 


When it should be 600.

thanks in advance
解决方案
In IEEE-754 binary double, we need to consider 1.1 and 1.2 in the binary representation:
1.2 = 0b1.001100110011001100110011001100110011001100110011001100110011...
1.1 = 0b1.000110011001100110011001100110011001100110011001100110011001...
note that we need infinitely many bits to represent them exactly in binary. double only has 53 bits of significance, we have to chop off the numbers:
1.2 = 0b1.001100110011001100110011001100110011001100110011001100110011...
1.1 = 0b1.000110011001100110011001100110011001100110011001100110011001...
                                                              ^ round from here
==>
1.2 ~ 0b1.0011001100110011001100110011001100110011001100110011
      (= exactly 1.1999999999999999555910790149937383830547332763671875)
1.1 ~ 0b1.0001100110011001100110011001100110011001100110011010
      (= exactly 1.100000000000000088817841970012523233890533447265625)
Hence 1.2 - 1.1 is:
  1.2 ~ 0b1.0011001100110011001100110011001100110011001100110011
- 1.1 ~ 0b1.0001100110011001100110011001100110011001100110011010
————————————————————————————————————————————————————————————————
        0b0.00011001100110011001100110011001100110011001100110010000
        (= exactly 0.09999999999999986677323704498121514916419982910156250000)
We can actually compute 60 / 0.0999999999999998667732370449812151491641998291015625 exactly, which gives
600.0000000000007993605777301137740672368493927467455286920109359612256820927...
                ^ 16th significant figure
that matches OP's result of
600.0000000000008


                        
这篇关于Java Double变量有奇怪的值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！