将浮点数转换为双倍，而不会损失精度 [英] Convert float to double without losing precision

问题描述

我有一个原始的浮动，我需要一个原始的双重。简单地将浮动物投射到双倍，给我奇怪的额外的精度。例如：

  float temp = 14009.35F; 
 System.out.println（Float.toString（temp））; // Prints 14009.35 
 System.out.println（Double.toString（（double）temp））; //打印14009.349609375 
  

但是，如果代替转换，我将float作为字符串输出，并解析该字符串为双，我得到我想要的：

  System.out.println（Double.toString（Double.parseDouble Float.toString（TEMP））））; 
 //打印14009.35 
  

有没有比String更好的方法？

解决方案

这不是你实际获得额外的精度 - 这是浮动没有准确地代表你原本打算的号码。双重 正好代表原始浮标; toString 正在显示已经存在的额外数据。

例如（这些数字不是对，我只是做的事情）支持你有：

  float f = 0.1F; 
 double d = f; 
  

然后， f 的值可能正好0.100000234523。 d 将具有完全相同的值，但是当您将其转换为字符串时，它将信任准确到更高的精度，因此不会像早期，你会看到已经在那里的额外的数字，但隐藏了你。

当你转换成一个字符串并返回时，你结束了一个比原始浮点数更接近字符串值的双精度值，但这只是很好的如果你真的相信字符串值是你真正想要的。

你确定float / double是这里使用的适当类型，而不是 BigDecimal ？如果您尝试使用具有精确十进制值（例如金钱）的数字，则 BigDecimal 是一种更合适的类型IMO。

I have a primitive float and I need as a primitive double. Simply casting the float to double gives me weird extra precision. For example:

float temp = 14009.35F;
System.out.println(Float.toString(temp)); // Prints 14009.35
System.out.println(Double.toString((double)temp)); // Prints 14009.349609375

However, if instead of casting, I output the float as a string, and parse the string as a double, I get what I want:

System.out.println(Double.toString(Double.parseDouble(Float.toString(temp))));
// Prints 14009.35

Is there a better way than to go to String and back?

解决方案

It's not that you're actually getting extra precision - it's that the float didn't accurately represent the number you were aiming for originally. The double is representing the original float accurately; toString is showing the "extra" data which was already present.

For example (and these numbers aren't right, I'm just making things up) support you had:

float f = 0.1F;
double d = f;

Then the value of f might be exactly 0.100000234523. d will have exactly the same value, but when you convert it to a string it will "trust" that it's accurate to a higher precision, so won't round off as early, and you'll see the "extra digits" which were already there, but hidden from you.

When you convert to a string and back, you're ending up with a double value which is closer to the string value than the original float was - but that's only good if you really believe that the string value is what you really wanted.

Are you sure that float/double are the appropriate types to use here instead of BigDecimal? If you're trying to use numbers which have precise decimal values (e.g. money), then BigDecimal is a more appropriate type IMO.

这篇关于将浮点数转换为双倍，而不会损失精度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！