Java 精度损失

发布于 2024-08-24 05:20:34 字数 534 浏览 4 评论 0原文

我有一个关于精度损失的问题，

我的任务是将数字打印为字符串

int exponent = ...
int[] Mantissas = { 1, 2, 5 };
double dataStep = java.lang.Math.pow(10.0, exponent) * Mantissas[mantissaIndex];
...
for (int i = 0; i < NSteps; i++)
                    steps[i] = firstStep + i * dataStep;
draw(steps);

，例如 0.2*7=1.4000000000000001; 0.0000014/10=1.3999999999999998E-7

如何解决这个问题？

UPD：主要问题是字符串输出格式。我不担心丢失大约 0.00000001 的值。现在我将其解决为 String.format("%f", value), 但我认为这不是好方法

原文

I have a problem concerned with losing of precision

my task is to print numbers as strings

int exponent = ...
int[] Mantissas = { 1, 2, 5 };
double dataStep = java.lang.Math.pow(10.0, exponent) * Mantissas[mantissaIndex];
...
for (int i = 0; i < NSteps; i++)
                    steps[i] = firstStep + i * dataStep;
draw(steps);

for example, 0.2*7=1.4000000000000001; 0.0000014/10=1.3999999999999998E-7

how to figure out this problem?

UPD: The main problem is string output formating. i don't bother about losting of about 0.00000001 value.
Now I solved it as String.format("%f", value),
but I think it's not good approach

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夜血缘 2024-08-31 05:20:34

正如其他人提到的，您必须使用 java.math.BigDecimal 而不是 float/double。然而，这也带来了一系列问题。

例如，当您调用 BigDecimal(double) 时，您传入的值将扩展为其完整表示形式：

BigDecimal oneTenth = new BigDecimal(0.1);
BigDecimal oneMillion = new BigDecimal(1000000);
oneTenth.multiply(oneMillion)
out> 100000.0000000000055511151231257827021181583404541015625000000

但是，当您使用 BigDecimal(String) 构造函数时，将表示 eact 值，并且您

BigDecimal oneTenth = new BigDecimal("0.1");
BigDecimalr oneMillion = new BigDecimal(1000000);
oneTenth.multiply(oneMillion)
out> 100000.0

可以在 Joshua Bloch 中阅读有关 BigDecimal 限制的更多信息以及 Neal Gafter 精彩的 Java puzzlers 书籍和这篇内容丰富的文章。最后请注意，BigDecimal 上的 toString 将以科学计数法打印，因此您必须正确使用 toPlainString 来代替。

As mentioned by others you have to use java.math.BigDecimal instead of float/double. This however comes with its own set of problems.

For instance when you call BigDecimal(double) the value you pass in will be expanded to its full representation:

BigDecimal oneTenth = new BigDecimal(0.1);
BigDecimal oneMillion = new BigDecimal(1000000);
oneTenth.multiply(oneMillion)
out> 100000.0000000000055511151231257827021181583404541015625000000

But when you use the BigDecimal(String) constructor the eact value is represented and you get

BigDecimal oneTenth = new BigDecimal("0.1");
BigDecimalr oneMillion = new BigDecimal(1000000);
oneTenth.multiply(oneMillion)
out> 100000.0

You can read more on BigDecimal's limitations in Joshua Bloch and Neal Gafter's splendid Java puzzlers book and in this informative article. Finally note that toString on BigDecimal's will print in scientific notation so you will properly have to use toPlainString instead.

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