Java的双重计算 [英] java double calculation
问题描述
我知道计算机不能精确地表示非整数.因此，当我在Java中添加2个双打时:
I understand that computer can not represent non-integral numbers precisely. so when I add 2 doubles in java for example:
724.64d + 1000d
控制台打印出1724.6399999999999
the console print out 1724.6399999999999
但是为什么要使用 724.64d + 100d 和 724.64d + 10000d
控制台分别打印出824.64和10724.64吗?
the console print out 824.64 and 10724.64 separately?
当我将两个双打相加时，有什么方法可以知道在什么条件下，总和就是确切的数字吗?
is there a way to know at what condition when I add the 2 doubles, the sum is the exact number ?
之所以问，是因为我们的旧程序使用double进行计算.并使用双重比较来验证数字.例如:让我们说总数为 1849.64 ，所有输入的总和必须等于总数为 1849.64
The reason why I ask is because that our old program use double to do calculation. and use double comparison to validate the numbers.
for example: let us say the total is 1849.64, all the inputs amounts added up must be equals to total which is 1849.64
input 1: 724.64
input 2: 1125
将不起作用，因为总和为1849.6399999999999
will not work, because the sum will be 1849.6399999999999
但是如果我们在下面这样输入，则总和为1849.64
but if we input like this below will work, and the sum is 1849.64
input 1: 24.64
input 2: 1825
那么如何找到有效的组合呢?注意，我无权访问此特定的非常旧的程序.当验证失败时，我们必须像第二个输入组合一样手动找到一个四处走动.谢谢.
so how to find those combinations that work? Note, I do not have access to this specific very old program. when the validation failed, we have to manually find a walk around like the second inputs combination. Thanks.
推荐答案
BigDecimal bigDecimal = new BigDecimal(724.64);
bigDecimal = bigDecimal.add(new BigDecimal(1000.0));
System.out.println(bigDecimal.floatValue());<--Works fine
System.out.println(bigDecimal.doubleValue());<--Works as mentioned in Question
输出:
1724.64
1724.6399999999999
在第一种情况下，它起作用是因为发生了缩小原始转换的情况.但是使用浮点数，您将不得不接受并接受它.
In the first case it works because of narrowing primitive conversion happens. But with Floating-Point numbers you will have to accept and live with it.
正如我所说的，它对于基本体有效的原因
As I stated the reason it is valid for primitives
double d = 724.64;
double d1 = 1000.0;
System.out.println(d + d1);
System.out.println((float) (d + d1));
输出:
1724.64
1724.6399999999999
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