Return the factorial value of the input. - Java java.lang

Java examples for java.lang:Math Value

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Description

Return the factorial value of the input.

Demo Code


//package com.java2s;
import java.math.BigInteger;

public class Main {
    /** Return the factorial value of the input.
     * Note: Numbers can quickly overwhelm the MAX_LONG and cause wrap-around.
     * Note: Currently, negative numbers are not supported and will throw an IllegalArgumentException. */
    public static BigInteger factorial(long num) {
        if (num < 0) {
            throw new IllegalArgumentException("Input must be non-negative");
        }/*from   www .  j  a  v a 2 s  .co  m*/
        if (num == 0) {
            return BigInteger.ONE;
        } // Source: http://mathforum.org/dr.math/faq/faq.0factorial.html

        BigInteger product = BigInteger.ONE;
        for (BigInteger i = new BigInteger("" + num); i
                .compareTo(BigInteger.ZERO) > 0; i = i
                .subtract(BigInteger.ONE)) {
            product = product.multiply(i);
        }
        System.out.println("factorial(" + num + ")=" + product);
        return product;
    }
}

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