如何四舍五入到最接近的 10 或 100 或 x

Question

How to round up to the nearest 10 (or 100 or X)?

这个link提供了r中问题的解决方案，我们如何在java中实现类似的东西？

这不是简单的四舍五入的情况，而是根据值本身进行的有点复杂的四舍五入，例如0.0322 至 0.04， 3.22至4， 32.2 至 40， 42.2 至 50 和 422.2 到 500。

Answer 1

我想不出为什么这个问题被否决的原因有很多，特别是因为没有说 "X" 必须是 10 的效力。

如果您的 "X" 意味着效力为 10，您可能会发现 Enum RoundingMode 和类 MathContext 和 BigDecimal 很有帮助。详情请见 https://docs.oracle.com/javase/8/docs/api/

无论如何：此 Java 方法处理 any rounding-base greater one 的舍入 int：

int round(int num, 
          int base /* "X", MUST be greater than 1 */, 
          boolean roundMiddleUp /* true is usual in business calculations */) {
    int lower = (num / base) * base - (num < 0 ? base: 0);
    int upper = lower + base;

    int difLower = Math.abs(num - lower);
    int difUpper = Math.abs(num - upper);
    int rounded = (difLower < difUpper) ? lower : (difLower != difUpper) ? upper : roundMiddleUp ? upper : lower;
    return rounded;
}

希望对您有所帮助。

Answer 2

请试试这个公式

System.out.println(Math.ceil(x*Math.pow(10, -Math.floor(Math.log10(x)))) / Math.pow(10, -Math.floor(Math.log10(x))) ) ; 你可以试试这个公式 online.

class Main {
    public static void niceround(double x) {
        System.out.println(x+" to " + Math.ceil(x * Math.pow(10, -Math.floor(Math.log10(x)))) / Math.pow(10, -Math.floor(Math.log10(x))));
    }
    public static void main(String[] args) {
        niceround(0.0322);
        niceround(3.22);
        niceround(32.2);
        niceround(42.2);
        niceround(422.2);
    }
}

测试

/usr/lib/jvm/java-1.8.0-openjdk-amd64/bin/java -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:36808,suspend=y,server=n -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/charsets.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/icedtea-sound.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jce.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/jsse.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/management-agent.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/resources.jar:/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/lib/rt.jar:/home/dac/proj/javatest2016/out/production/javatest2016:/home/dac/Downloads/idea-IU-145.972.3/lib/idea_rt.jar Main
Connected to the target VM, address: '127.0.0.1:36808', transport: 'socket'
0.0322 to 0.04
3.22 to 4.0
32.2 to 40.0
42.2 to 50.0
422.2 to 500.0
Disconnected from the target VM, address: '127.0.0.1:36808', transport: 'socket'

Process finished with exit code 0

如何四舍五入到最接近的 10 或 100 或 x

How to round up to nearest 10 or 100 or x

java

rounding