减去两个十进制数给出奇怪的输出 [英] Subtracting two decimal numbers giving weird outputs

问题描述

当我用Java Puzzlers的代码（我没有这本书）的时候，我碰到了这段代码

  public static void main（String args []）{
 System.out.println（2.00  -  1.10）; 
 
 $ / code> 

输出是



  0.8999999999999999 
  

当我尝试将代码更改为

2.00d - 1.10d 仍然得到与 0.8999999999999999

对于 2.00d - 1.10f 输出是 0.8999999761581421

对于， 2.00f - 1.10d 输出是 0.8999999999999999

对于 2.00f - 1.10f 输出是 0.9

为什么不把输出作为 0.9 放在首位呢？我无法做出任何正面或反面的意见？有人可以说清楚这一点吗？

解决方案

在二进制0.1是0.00011001100110011001100110011001 .....，

因此，它不能完全用二进制表示。取决于你在哪里取整（float或double），你会得到不同的答案。

所以0.1f = 0.000110011001100110011001100
和0.1d = 0.0001100110011001100110011001100110011001100110011001

您注意到该数字在1100周期内重复。然而浮点数和双精度在循环中的不同点上分开。就这样，一个错误上来，另一个下来;导致差异。

但最重要的是，
永远不要假设浮点数是准确的

While I was having fun with codes from Java Puzzlers(I don't have the book) I came across this piece of code

public static void main(String args[]) {
        System.out.println(2.00 - 1.10);
    }

Output is

0.8999999999999999

When I tried changing the code to

2.00d - 1.10d still I get the same output as 0.8999999999999999

For,2.00d - 1.10f Output is 0.8999999761581421
For,2.00f - 1.10d Output is 0.8999999999999999
For,2.00f - 1.10f Output is 0.9

Why din't I get the output as 0.9 in the first place? I could not make any heads or tails out of this? Can somebody articulate this?

解决方案

In binary 0.1 is 0.00011001100110011001100110011001.....,

As such it cannot be represented exactly in binary. Depending where you round off (float or double) you get different answers.

So 0.1f =0.000110011001100110011001100 And 0.1d=0.0001100110011001100110011001100110011001100110011001

You note that the number repeats on a 1100 cycle. However the float and double precision split it at a different point in the cycle. As such on one the error rounds up and the other rounds down; leading to the difference.

But most importantly; Never assume floating point numbers are exact

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