Java Guava | Longs.factorial(int n) method with Examples

The factorial(int n) method of Guava’s LongMath Class returns the product of the first n positive integers, which is n!.

Syntax :

public static long factorial(int n)

Parameter: The method accepts only one parameter n which is of integer type and is to be used to find the factorial.

Return Value: This method return following values:

• This method returns 1 if n is 0.
• This method returns product of the first n positive integers if the result fits in a long.
• This method returns Long.MAX_VALUE if the result does not fit in a long.

Exceptions: The method factorial(int n) throws IllegalArgumentException if n is negative.

Below programs illustrate the use of LongMath.factorial() method:

Example 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);
    }
}

Output:

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

Example 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);
        }
    }
}

Output:

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

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