在Java中操作和比较浮点数 [英] Manipulating and comparing floating points in java

问题描述

在Java中，浮点运算没有精确表示。例如这个Java代码：

  float a = 1.2; 
 float b = 3.0; 
 float c = a * b; 
 if（c == 3.6）{
 System.out.println（c is 3.6）; 
} 
 else {
 System.out.println（c不是3.6）; 
} 
  

打印c不是3.6。

我对3位以下的精度不感兴趣（＃。###）。我怎样才能处理这个问题，以浮动乘法和比较可靠？

解决方案

这是一个普遍规则，浮点数不应该（a == b）进行比较，而是像（Math.abs（ab）其中 / em>是一个很小的数字。

具有十进制形式的固定位数的浮点值不需要二进制形式的固定位数。

另外为了清楚起见：

虽然严格 == 比较浮点数的实际意义很小，严格的< / code>和> 比较，相反，是有效的用例（例子 - 当某个值超过阈值时逻辑触发：（val> threshold）&& panic（）;


In Java the floating point arithmetic is not represented precisely. For example this java code:

float a = 1.2; 
float b= 3.0;
float c = a * b; 
if(c == 3.6){
    System.out.println("c is 3.6");
} 
else {
    System.out.println("c is not 3.6");
} 

Prints "c is not 3.6".

I'm not interested in precision beyond 3 decimals (#.###). How can I deal with this problem to multiply floats and compare them reliably?

解决方案

It's a general rule that floating point number should never be compared like (a==b), but rather like (Math.abs(a-b) < delta) where delta is a small number.

A floating point value having fixed number of digits in decimal form does not necessary have fixed number of digits in binary form.

Addition for clarity:

Though strict == comparison of floating point numbers has very little practical sense, the strict < and > comparison, on the contrary, is a valid use case (example - logic triggering when certain value exceeds threshold: (val > threshold) && panic();)

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