# Returns n!. Shorthand for n Factorial, the product of the numbers 1,...,n as a double. : Math Functions « Development « Java Tutorial

import java.io.File;

/*
* Licensed to the Apache Software Foundation (ASF) under one or more
*  contributor license agreements.  See the NOTICE file distributed with
*  The ASF licenses this file to You under the Apache License, Version 2.0
*  (the "License"); you may not use this file except in compliance with
*  the License.  You may obtain a copy of the License at
*
*
*  Unless required by applicable law or agreed to in writing, software
*  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
*  See the License for the specific language governing permissions and
*
*
*/
public class Main {
/**
* Returns n!. Shorthand for <code>n</code> <a
* href="http://mathworld.wolfram.com/Factorial.html"> Factorial</a>, the
* product of the numbers <code>1,...,n</code> as a <code>double</code>.
*
* <Strong>Preconditions</strong>:
* <ul>
* <li> <code>n >= 0</code> (otherwise
* <code>IllegalArgumentException</code> is thrown)</li>
* <li> The result is small enough to fit into a <code>double</code>. The
* largest value of <code>n</code> for which <code>n!</code> <
* Double.MAX_VALUE</code> is 170. If the computed value exceeds
* Double.MAX_VALUE, Double.POSITIVE_INFINITY is returned</li>
* </ul>
*
*
* @param n argument
* @return <code>n!</code>
* @throws IllegalArgumentException if n < 0
*/
public static double factorialDouble(final int n) {
if (n < 0) {
throw new IllegalArgumentException("must have n >= 0 for n!");
}
return Math.floor(Math.exp(factorialLog(n)) + 0.5);
}

/**
* Returns the natural logarithm of n!.
*
* <Strong>Preconditions</strong>:
* <ul>
* <li> <code>n >= 0</code> (otherwise
* <code>IllegalArgumentException</code> is thrown)</li>
* </ul>
*
* @param n argument
* @return <code>n!</code>
* @throws IllegalArgumentException if preconditions are not met.
*/
public static double factorialLog(final int n) {
if (n < 0) {
throw new IllegalArgumentException("must have n > 0 for n!");
}
double logSum = 0;
for (int i = 2; i <= n; i++) {
logSum += Math.log((double)i);
}
return logSum;
}

}
 6.17.Math Functions 6.17.1. Math Class Methods 6.17.2. Use math functions 6.17.3. Testing the Math class methods 6.17.4. Floating Point Number Enhancements in JDK 6 6.17.5. Math.scalb 6.17.6. Math.getExponent 6.17.7. Math.nextAfter 6.17.8. Math.nextUp 6.17.9. Math.copySign 6.17.10. Demonstrate toDegrees() and toRadians(). 6.17.11. Find absolute value of float, int, double and long using Math.abs 6.17.12. Find ceiling value of a number using Math.ceil 6.17.13. Find exponential value of a number using Math.exp 6.17.14. Find floor value of a number using Math.floor 6.17.15. Find maximum of two numbers using Math.max 6.17.16. Find natural logarithm value of a number using Math.log 6.17.17. Find power using Math.pow 6.17.18. Find square root of a number using Math.sqrt 6.17.19. Round Java float and double numbers using Math.round 6.17.20. Math.min 6.17.21. Normalizes an angle to a relative angle. 6.17.22. Normalizes an angle to an absolute angle. 6.17.23. Normalizes an angle to be near an absolute angle 6.17.24. Calculate the floor of the log, base 2 6.17.25. Greatest Common Divisor (GCD) of positive integer numbers 6.17.26. Least Common Multiple (LCM) of two strictly positive integer numbers 6.17.27. Moving Average 6.17.28. Normalize an angle in a 2&pi wide interval around a center value. 6.17.29. Returns n!. Shorthand for n Factorial, the product of the numbers 1,...,n as a double. 6.17.30. Returns n!. Shorthand for n Factorial, the product of the numbers 1,...,n. 6.17.31. Returns the hyperbolic cosine of x. 6.17.32. Returns the hyperbolic sine of x. 6.17.33. Returns the natural log of the (http://mathworld.wolfram.com/BinomialCoefficient.html) Binomial Coefficient 6.17.34. Returns the natural logarithm of n!. 6.17.35. Round the given value to the specified number of decimal places. The value is rounded using the BigDecimal.ROUND_HALF_UP method. 6.17.36. Value is rounded using the given method which is any method defined in BigDecimal 6.17.37. sqrt(a^2 + b^2) without under/overflow