Java BigIntegerMath log10() 函数

Guava的BigIntegerMath类的方法 log10(BigInteger x, RoundingMode mode) 返回x的基10对数，并根据指定的四舍五入模式进行取舍。

语法

public static int log10(BigInteger x, RoundingMode mode)

参数。这个方法需要以下参数。

x : 要找到对数的BigInteger数字。
mode : 用于计算10的对数的四舍五入模式。

返回值。此方法返回x的以10为基数的对数，根据指定的四舍五入模式。

异常： 该方法会抛出以下异常。

IllegalArgumentException： 如果x<=0。
ArithmeticException： 如果模式是RoundingMode.UNNECESSARY并且x不是10的幂。

Enum RoundingMode

枚举常数	描述
CEILING	四舍五入模式，朝向正无穷大。
DOWN	向零舍入的舍入模式。
FLOOR	负无穷大的四舍五入模式。
HALF_DOWN	向 “最近的邻居 “舍入的舍入模式，除非两个邻居的距离相等，在这种情况下向下舍入。
HALF_EVEN	向 “最近的邻居 “舍入的舍入模式，除非两个邻居都是等距离，在这种情况下，向偶数邻居舍入。
HALF_UP	向 “最近的邻居 “舍入的舍入模式，除非两个邻居都是等距离，在这种情况下，向上舍入。
UNNECESSARY	四舍五入模式，断言请求的操作有一个精确的结果，因此不需要四舍五入。
UP	舍入模式，从零开始舍入。

下面的例子说明了 BigIntegerMath.log10() 方法。

例1 :

// Java code to show implementation of
// log10(BigInteger x, RoundingMode mode) method
// of Guava's BigIntegerMath class
  
import java.math.*;
import com.google.common.math.BigIntegerMath;
  
class GFG {
  
    // Driver code
    public static void main(String args[])
    {
        BigInteger a1 = BigInteger.valueOf(10000);
  
        // Using log10(BigInteger x, RoundingMode mode)
        // method of Guava's BigIntegerMath class
        // The RoundingMode HALF_EVEN rounds towards
        // the "nearest neighbor" unless both neighbors
        // are equidistant, in which case, round towards
        // the even neighbor.
        System.out.println("Log base 10 of " + a1
                           + " with rounding mode HALF_EVEN = "
                           + BigIntegerMath
                                 .log10(a1,
                                        RoundingMode.HALF_EVEN));
  
        BigInteger a2 = BigInteger.valueOf(15);
  
        // Using log10(BigInteger x, RoundingMode mode)
        // method of Guava's BigIntegerMath class
        // The RoundingMode HALF_DOWN rounds towards
        // "nearest neighbor" unless both neighbors
        // are equidistant, in which case round down.
        System.out.println("Log base 10 of " + a2
                           + " with rounding mode HALF_DOWN = "
                           + BigIntegerMath
                                 .log10(a2,
                                        RoundingMode.HALF_DOWN));
    }
}

输出。

Log base 10 of 10000 with rounding mode HALF_EVEN = 4
Log base 10 of 15 with rounding mode HALF_DOWN = 1

例2： 显示IllegalArgumentException

// Java code to show implementation of
// log10(BigInteger x, RoundingMode mode) method
// of Guava's BigIntegerMath class
  
import java.math.*;
import com.google.common.math.BigIntegerMath;
  
class GFG {
  
    // Driver code
    public static void main(String args[])
    {
  
        try {
            BigInteger a1 = BigInteger.valueOf(-5);
  
            // Using log10(BigInteger x, RoundingMode mode)
            // method of Guava's BigIntegerMath class
            // The RoundingMode HALF_EVEN rounds towards
            // the "nearest neighbor" unless both neighbors
            // are equidistant, in which case, round towards
            // the even neighbor.
            // This should throw "IllegalArgumentException"
            // as a1 <= 0
            System.out.println("Log base 10 of " + a1
                               + " with rounding mode HALF_EVEN = "
                               + BigIntegerMath
                                     .log10(a1,
                                            RoundingMode.HALF_EVEN));
        }
  
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

输出。

Exception: java.lang.IllegalArgumentException: x (-5) must be > 0

参考资料: https://google.github.io/guava/releases/21.0/api/docs/com/google/common/math/BigIntegerMath.html#log10-java.math.BigInteger-java.math.RoundingMode-