問(wèn)題描述
可能重復(fù):
在java中使用雙精度保持精度
Java 程序中奇怪的浮點(diǎn)行為
我正在制作一個(gè)直方圖類，但遇到了一個(gè)奇怪的問(wèn)題.
I'm making a histogram class, and I'm encountering a weird issue.
這是該類的基礎(chǔ)知識(shí)，還有更多方法，但與問(wèn)題無(wú)關(guān).
Here are the basics of the class, there are more methods but they aren't relevant to the issue.
private int[] counters;
private int numCounters;
private double min, max, width;
public Histogram(double botRange, double topRange, int numCounters) {
counters = new int[numCounters];
this.numCounters = numCounters;
min = botRange;
max = topRange;
width = (max - min) / (double) numCounters;
}
public void plotFrequency() {
for (int i = 0; i < counters.length; i++) {
writeLimit(i * width, (i + 1) * width);
System.out.println(counters[i]);
}
}
private void writeLimit(double start, double end) {
System.out.print(start + " <= x < " + end + " ");
}
當(dāng)我繪制頻率時(shí)會(huì)出現(xiàn)問(wèn)題.我創(chuàng)建了 2 個(gè)實(shí)例.新直方圖(0, 1, 10);新直方圖(0, 10, 10);
the problem happens when I plot the frequencies. I've created 2 instances. new Histogram(0, 1, 10); new Histogram(0, 10, 10);
這是他們輸出的內(nèi)容.
Frequecy
0.0 <= x < 0.1 989
0.1 <= x < 0.2 1008
0.2 <= x < 0.30000000000000004 1007
0.30000000000000004 <= x < 0.4 1044
0.4 <= x < 0.5 981
0.5 <= x < 0.6000000000000001 997
0.6000000000000001 <= x < 0.7000000000000001 1005
0.7000000000000001 <= x < 0.8 988
0.8 <= x < 0.9 1003
0.9 <= x < 1.0 978
Frequecy
0.0 <= x < 1.0 990
1.0 <= x < 2.0 967
2.0 <= x < 3.0 1076
3.0 <= x < 4.0 1048
4.0 <= x < 5.0 971
5.0 <= x < 6.0 973
6.0 <= x < 7.0 1002
7.0 <= x < 8.0 988
8.0 <= x < 9.0 1003
9.0 <= x < 10.0 982
所以我的問(wèn)題是，為什么我在第一個(gè)示例中得到了非常長(zhǎng)的小數(shù)限制，而在第二個(gè)示例中沒(méi)有?
So my question is, why am I getting the really long decimal limits in the first example, but not the second one?
推薦答案
有些小數(shù)不能用雙精度值精確表示.0.3 是這些值之一.
Some decimals cannot be exactly represented by double values. 0.3 is one of those values.
所有小于某個(gè)數(shù)字(我忘記了)的整數(shù)值恰好有一個(gè)雙精度值的精確表示，所以你看不到近似值.
All integer values less than a certain number (I forget which) happen to have an exact representation by a double value, so you don't see the approximation.
考慮我們?nèi)绾慰创龜?shù)字:數(shù)字 123 表示為 (1 * 100) + (2 * 10) + (3 * 1).我們使用 10 作為我們的基礎(chǔ).二進(jìn)制數(shù)使用兩個(gè).因此，當(dāng)您查看數(shù)字的分?jǐn)?shù)時(shí)，如何通過(guò)添加 2 的單個(gè)冪來(lái)表示 0.3?你不能.你能想到的最好的值大約是 0.30000000000000004(我必須查看確切的二進(jìn)制數(shù)字才能知道它是如何達(dá)到的).
Consider how we think of numbers: the number 123 is represented as (1 * 100) + (2 * 10) + (3 * 1). We use 10 as our base. Binary numbers use two. So when you look at fractions of a number, how could you represent 0.3 by adding individual powers of 2? You can't. The best you can come up with is about 0.30000000000000004 (I'd have to see the exact binary digits to see how it reaches that).
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