Guava – LongMath.log10方法与实例
Guava的LongMath类的log10(long x, RoundingMode mode)方法接受两个参数,根据第二个参数指定的舍入模式计算第一个参数的基10对数值。
语法:
public static int log10(long x, RoundingMode mode)
参数: 该方法接受2个参数。
- x 是要找到对数的长值。
- mode 是指定的舍入模式。
返回值: 该方法返回x的Base-10对数,根据指定的四舍五入模式进行四舍五入。
异常情况: 此方法抛出以下参数。
- IllegalArgumentException:如果x的值是0或负值。
- ArithmeticException:如果模式是RoundingMode.UNNECESSARY并且x不是10的幂。
Enum RoundingMode
Enum Constant | Description |
---|---|
CEILING | 向正无穷大舍入的舍入模式。 |
DOWN | 向零舍入的舍入模式。 |
FLOOR | 四舍五入到负无穷大的模式。 |
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 “四舍五入的模式,除非两个邻居都是等距离,在这种情况下,向偶数邻居四舍五入。 |
HALF_UP | 向 “最近的邻居 “四舍五入的模式,除非两个邻居都是等距离的,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 | 四舍五入模式是指从零开始舍入。 |
下面给出了一些例子,以便更好地理解实现:
示例1:
// Java code to show implementation of
// log10(long x, RoundingMode mode) method
// of Guava's LongMath class
import java.math.RoundingMode;
import com.google.common.math.LongMath;
class GFG {
// Driver code
public static void main(String args[])
{
long a1 = 10000;
// Using log10(long x, RoundingMode mode)
// method of Guava's LongMath 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(
LongMath.log10(
a1,
RoundingMode.HALF_EVEN));
long a2 = 15;
// Using log10(long x, RoundingMode mode)
// method of Guava's LongMath class
// The RoundingMode HALF_DOWN rounds towards
// "nearest neighbor" unless both neighbors
// are equidistant, in which case round down.
System.out.println(
LongMath.log10(a2,
RoundingMode.HALF_DOWN));
}
}
输出:
4
1
例2:
// Java code to show implementation of
// log10(long x, RoundingMode mode) method
// of Guava's LongMath class
import java.math.RoundingMode;
import com.google.common.math.LongMath;
class GFG {
static int findlog10(long x, RoundingMode mode)
{
try {
// Using log10(long x, RoundingMode mode)
// method of Guava's LongMath 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 x <= 0
int ans = LongMath.log10(x, mode);
// Return the answer
return ans;
}
catch (Exception e) {
System.out.println(e);
return -1;
}
}
// Driver code
public static void main(String args[])
{
long x = -122;
try {
// Function calling
findlog10(x, RoundingMode.HALF_EVEN);
}
catch (Exception e) {
System.out.println(e);
}
}
}
输出:
java.lang.IllegalArgumentException: x (-122) must be > 0
参考: https://google.github.io/guava/releases/20.0/api/docs/com/google/common/math/LongMath.html#log10-long-java.math.RoundingMode-