Guava – Longs.factorial方法与实例

Guava的LongMath类的factorial(int n)方法返回前n个正整数的乘积，也就是n！。

语法:

public static long factorial(int n)

参数: 该方法只接受一个参数 n ，该参数为整数类型，用于求阶乘。

返回值： 本方法返回以下数值。

• 本方法返回 1 if n is 0.
• 本方法返回前n个正整数的乘积，如果结果适合于long。
• 如果结果不在一个长条中，该方法返回 Long.MAX_VALUE 。

异常情况： 阶乘(int n)方法如果n是负数，会产生IllegalArgumentException。

以下程序说明了LongMath.factorial()方法的使用。

示例1:

// Java code to show implementation of
// factorial(int n) 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[])
    {
        int n1 = 10;
  
        // Using factorial(int n) method of
        // Guava's LongMath class
        long ans1 = LongMath.factorial(n1);
  
        System.out.println("factorial of "
                           + n1 + " is : "
                           + ans1);
  
        int n2 = 12;
  
        // Using factorial(int n) method of
        // Guava's LongMath class
        long ans2 = LongMath.factorial(n2);
  
        System.out.println("factorial of "
                           + n2 + " is : "
                           + ans2);
    }
}

输出:

factorial of 10 is : 3628800
factorial of 12 is : 479001600

示例 2 :

// Java code to show implementation of
// factorial(int n) method of Guava's
// LongMath Class
  
import java.math.RoundingMode;
import com.google.common.math.LongMath;
  
class GFG {
  
    static long findFact(int n)
    {
        try {
            // Using factorial(int n) method of
            // Guava's LongMath class
            // This should throw "IllegalArgumentException"
            // as n < 0
            long ans = LongMath.factorial(n);
  
            // Return the answer
            return ans;
        }
        catch (Exception e) {
            System.out.println(e);
            return -1;
        }
    }
  
    // Driver code
    public static void main(String args[])
    {
        int n = -5;
  
        try {
  
            // Function calling
            findFact(n);
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

输出:

java.lang.IllegalArgumentException: n (-5) must be >= 0

参考:

https://google.github.io/guava/releases/20.0/api/docs/com/google/common/math/LongMath.html#factorial-int-