java - double 或 float 数据类型在循环中不能正确相加？

Question

在一个循环中，我添加 0.10 直到达到所需的 #，并获取索引。这是我的代码:

    private static int getIndexOfUnits(float units) {
    int index = -1;
    float addup = 0.10f;
    for(float i = 1.00f; i < units; i=(float)i+addup) {
        index++;
        System.out.println("I = " + i + " Index = " + index);
    }

    return index;
}

如果通过的单位是 5.7，我看到的输出是:

I = 1.0 Index = 0
I = 1.1 Index = 1
I = 1.2 Index = 2
I = 1.3000001 Index = 3
I = 1.4000001 Index = 4
I = 1.5000001 Index = 5
I = 1.6000001 Index = 6
I = 1.7000002 Index = 7
I = 1.8000002 Index = 8
I = 1.9000002 Index = 9
I = 2.0000002 Index = 10
I = 2.1000001 Index = 11
I = 2.2 Index = 12
I = 2.3 Index = 13
I = 2.3999999 Index = 14
I = 2.4999998 Index = 15
I = 2.5999997 Index = 16
I = 2.6999996 Index = 17
I = 2.7999995 Index = 18
I = 2.8999994 Index = 19
I = 2.9999993 Index = 20
I = 3.0999992 Index = 21
I = 3.199999 Index = 22
I = 3.299999 Index = 23
I = 3.399999 Index = 24
I = 3.4999988 Index = 25
I = 3.5999987 Index = 26
I = 3.6999986 Index = 27
I = 3.7999985 Index = 28
I = 3.8999984 Index = 29
I = 3.9999983 Index = 30
I = 4.0999985 Index = 31
I = 4.1999984 Index = 32
I = 4.2999983 Index = 33
I = 4.399998 Index = 34
I = 4.499998 Index = 35
I = 4.599998 Index = 36
I = 4.699998 Index = 37
I = 4.799998 Index = 38
I = 4.8999977 Index = 39
I = 4.9999976 Index = 40
I = 5.0999975 Index = 41
I = 5.1999974 Index = 42
I = 5.2999973 Index = 43
I = 5.399997 Index = 44
I = 5.499997 Index = 45
I = 5.599997 Index = 46
I = 5.699997 Index = 47

如果单位是大数字，如 18.90 或 29.90，它会给出错误的索引。索引通常比应有的少 1。最初只添加了 0.10，但在 2.3 之后，它得到 2.39999.... 添加 0.10。我相信这是一个精确的问题。如何处理它并确保无论使用 float 还是 double，我都能在大 # 上获得正确的索引。

任何想法!!!!

Answer 1

来自Floating-Point Guide :

Why don’t my numbers, like 0.1 + 0.2 add up to a nice round 0.3, and instead I get a weird result like 0.30000000000000004?

Because internally, computers use a format (binary floating-point) that cannot accurately represent a number like 0.1, 0.2 or 0.3 at all.

When the code is compiled or interpreted, your “0.1” is already rounded to the nearest number in that format, which results in a small rounding error even before the calculation happens.

如果您需要数字加起来精确，则不能使用float 或double。请改用 BigDecimal。