问题描述
我有兴趣拥有以下 getNumberOfDecimalPlace 功能：
I was interested to have the following getNumberOfDecimalPlace function:
System.out.println("0 = " + Utils.getNumberOfDecimalPlace(0)); // 0
System.out.println("1.0 = " + Utils.getNumberOfDecimalPlace(1.0)); // 0
System.out.println("1.01 = " + Utils.getNumberOfDecimalPlace(1.01)); // 2
System.out.println("1.012 = " + Utils.getNumberOfDecimalPlace(1.012)); // 3
System.out.println("0.01 = " + Utils.getNumberOfDecimalPlace(0.01)); // 2
System.out.println("0.012 = " + Utils.getNumberOfDecimalPlace(0.012)); // 3
我可以知道如何实现 getNumberOfDecimalPlace ，使用 BigDecimal ？
May I know how can I implement getNumberOfDecimalPlace, by using BigDecimal?
以下代码无法按预期工作：
The following code doesn't work as expected:
public static int getNumberOfDecimalPlace(double value) {
final BigDecimal bigDecimal = new BigDecimal("" + value);
final String s = bigDecimal.toPlainString();
System.out.println(s);
final int index = s.indexOf('.');
if (index < 0) {
return 0;
}
return s.length() - 1 - index;
}
以下内容打印：
0.0
0 = 1
1.0
1.0 = 1
1.01
1.01 = 2
1.012
1.012 = 3
0.01
0.01 = 2
0.012
0.012 = 3
但是，对于案例0,1.0，它不能很好地工作。我期待，结果是0。但结果却是0.0和1.0。这将返回1。
However, for case 0, 1.0, it doesn't work well. I expect, "0" as result. But they turned out to be "0.0" and "1.0". This will return "1" as result.
推荐答案
此代码：
int getNumberOfDecimalPlaces(BigDecimal bigDecimal) {
String string = bigDecimal.stripTrailingZeros().toPlainString();
int index = string.indexOf(".");
return index < 0 ? 0 : string.length() - index - 1;
}
...通过这些测试：
... passes these tests:
assertThat(getNumberOfDecimalPlaces(new BigDecimal("0.001")), equalTo(3));
assertThat(getNumberOfDecimalPlaces(new BigDecimal("0.01")), equalTo(2));
assertThat(getNumberOfDecimalPlaces(new BigDecimal("0.1")), equalTo(1));
assertThat(getNumberOfDecimalPlaces(new BigDecimal("1.000")), equalTo(0));
assertThat(getNumberOfDecimalPlaces(new BigDecimal("1.00")), equalTo(0));
assertThat(getNumberOfDecimalPlaces(new BigDecimal("1.0")), equalTo(0));
assertThat(getNumberOfDecimalPlaces(new BigDecimal("1")), equalTo(0));
assertThat(getNumberOfDecimalPlaces(new BigDecimal("10")), equalTo(0));
assertThat(getNumberOfDecimalPlaces(new BigDecimal("10.1")), equalTo(1));
assertThat(getNumberOfDecimalPlaces(new BigDecimal("10.01")), equalTo(2));
assertThat(getNumberOfDecimalPlaces(new BigDecimal("10.001")), equalTo(3));
...如果这确实是你想要的。其他回复是正确的，你必须一直使用BigDecimal而不是double / float。
... if that is indeed what you want. The other replies are correct, you have to use BigDecimal all the way through for this rather than double/float.
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