# What is a “factorial program” and what are the related Java functions?

Hi,

I’m new to Java and I’m trying to write a program that calculates the factorial of an integer. Any help would be great.

Thanks,

P.S. What is a “factorial program” and what are the related Java functions?

Factorial is a mathematical operation, denoted by an exclamation point (!), that stands for the product of all the integers less than or equal to a given integer and greater than or equal to 1. For example, 5! (pronounced “five factorial”) is 5 * 4 * 3 * 2 * 1, which equals 120.

A factorial program in Java is one that uses the Java language to return the factorial of a given number. The related functions in Java are:

Math.factorial()

Math.factorialInt()

Math.factorialLong()

The factorial of a number N is defined as the product of all integers from 1 to N.

For example, 5! = 1*2*3*4*5 = 120.

The factorial function is often used in probability and statistics for various distributions like permutations and combinations.

Java does not have a built-in factorial function but it does support the math package which can be used to perform complex mathematical calculations including factorials.

This tutorial will discuss how to write the factorial code in Java, provide several examples, and outline some of the best practices when using Java.

Factorial program in java with examples of fibonacci series, armstrong number, prime number, palindrome number, factorial number, bubble sort, selection sort, insertion sort, swapping numbers etc.

Factorial program in java using methods

Factorial is a product of all positive descending integer begins with a specified number (n) and calculates up to one.

Example: factorial of 4 is 24 (1 x 2 x 3 x 4).The factorial of 0 is 1.

In this example we are going to use while loop to calculate the factorial of a given number. This program works as follows: at first the computer reads a number from the user. Then it checks whether the given input number is less than zero or not. If it is less than zero then an error message will be printed on the screen. Otherwise for loop will be executed to find the factorial of the given number.

The factorial function is defined as follows:

factorial(n) = n*factorial(n-1)

factorial(0) = 1

Therefore, the factorial of any number is that number multiplied by the factorial of (that number minus 1), with the special case that any number multiplied by 0 is 0.

The Java “for” keyword makes a looping construct where a variable is initialized, set to some end-point, and then modified in a certain way each time through the loop. The following example shows how this might be used:

public int factorial(int n){

for(int i=n;i>0;i–){//while i>0, multiply answer by i and then decrement i.

}

Factorials are commonly used in probability theory. The factorial of a positive integer n, written n!, is the product of all positive integers less than or equal to n:

n! = 1×2×3×…×n = 1 × 2 × 3 × … × n = 1\times2\times3\times…\times n = 1 × 2 × 3 × … × n

For example,

6!=1×2×3×4×5×6=1\times2\times3\times4\times5\times6=1 × 2 × 3 × 4 × 5 × 6

In Java, you can use the factorial function from the BigInteger class to calculate factorials for large values of n. For example, the statement below calculates the factorial of 100 and stores it in a BigInteger object:

BigInteger hundredFactorial = BigInteger.ONE;

for (int i = 2; i <= 100; i++){ hundredFactorial = hundredFactorial.multiply(BigInteger.valueOf(i)); } The factorial of a number is the product of all integers up to and including that number, so the factorial of 4 (written "4!") is 4x3x2x1 = 24. public class Factorial { public static void main(String[] args) { System.out.println(factorial(4)); // displays 24 } public static int factorial(int n) { if (n == 1) { // base case: 1! = 1 return 1; } else { // recursive case: n! = n * (n-1)! return n * factorial(n-1); } }// end class Factorial