Write a Factorial Program in Java Programming Language using For Loop, While Loop, Functions, and Recursion.

## Java Factorial Program using For Loop

This program for factorial allows the user to enter any integer value. By using this value, this Java program finds Factorial of a number using the For Loop.

The Factorial of number is the product of all the numbers less than or equal to that number & greater than 0. It is denoted with a (!) symbol. The mathematical representation of the Factorial is as shown below:

n! = n * (n-1) * (n -2) * …….* 1

For example, five Factorial is represented as 5! = 5 * 4 * 3 * 2 * 1 = 120

// Factorial Program in Java using For Loop package FrequentPrograms; import java.util.Scanner; public class FactorialNumberUsingFor { private static Scanner sc; public static void main(String[] args) { int i, Number; long Factorial = 1; sc = new Scanner(System.in); System.out.println(" Please Enter any number to Find Factorial: "); Number = sc.nextInt(); for (i = 1; i <= Number; i++) { Factorial = Factorial * i; } System.out.format("\nFactorial of %d = %d\n", Number, Factorial); } }

**OUTPUT**

**ANALYSIS**

In this factorial program in Java, First, We declared two integer variables i and number. We also declared one long variable Factorial and the assigned value of 1.

int i, Number; long Factorial = 1;

**NOTE: **Although we are calculating the factorial of an integer variable, we declared output (Factorial) as a long variable. Because, when we are writing a Java program for calculating the factorial for large integers, the result will cross the integer limit.

The following System.out.println statement will ask the user to enter his/her own integer value to calculate the factorial. Next, we are assigning the user entered value to the Number variable

System.out.println(" Please Enter any number to Find Factorial: "); Number = sc.nextInt();

Within the For Loop, We initialized the integer I value to 1 and also (i <= Number) condition will help the loop to terminate when the condition fails.

for (i = 1; i <= Number; i++) { Factorial = Factorial * i; }

Let us see the working principle of this Java factorial program for loop in iteration wise. From the above screenshot, you can observe that the user entered the value: Number = 4 and as we know i = 10 and Factorial = 1.

**First Iteration**

- Condition inside the For loop (1 <= 4) is True. So, the program will start executing statements inside the for loop
- Factorial = Factorial * i;
- Factorial = 1 *1 = 1
- Lastly, i will increment to 1. It means i will become 2. Please refer Increment and Decrement Operators article to understand the ++ notation.

**Second Iteration**

From the first iteration, i became 2 and Factorial = 1

- Condition inside the For loop (2 <= 4) is True. So, the Java Factorial program will start executing statements inside the for loop
- Factorial = 1 *2 = 2
- Lastly, i will increment to 1. It means i will become 3.

**Third Iteration**

From the second iteration, i = 3 and Factorial = 2

- For loop Condition (3 <= 4) is True
- Factorial = Factorial * i;
- Factorial = 2 *3 = 6
- Lastly, i will increment to 1. It means i will become 4.

**Fourth Iteration**

From the third iteration of Java factorial program, i = 4 and Factorial = 6

- Condition inside the For loop (4 <= 4) is True
- Factorial = 6 * 4 = 24
- Lastly, i incremented to 1. It means i will become 5.

**Fifth Iteration**

Condition inside the For loop (4 <= 4) is False so, For loop will be Terminated.

Last System.out.format statement will print the Factorial output of the user entered integer. Within the statement, the first %d refers to Number, and the second %d refers to Factorial.

System.out.format("\nFactorial of %d = %d\n", Number, Factorial);

### Factorial Program in Java using While Loop

This Java factorial program allows the user to enter any integer value. By using this value, this Java factorial program will find Factorial of a number using the While Loop

// Factorial Program in Java using While Loop package FrequentPrograms; import java.util.Scanner; public class FactorialNumberUsingWhile { private static Scanner sc; public static void main(String[] args) { int i = 1, Number; long Factorial = 1; sc = new Scanner(System.in); System.out.println(" Please Enter any number to Find Factorial: "); Number = sc.nextInt(); while (i <= Number) { Factorial = Factorial * i; i++; } System.out.format(" Factorial of %d = %d", Number, Factorial); } }

We just replaced the For loop in the above Java factorial program example with the While loop. If you do not understand the While Loop, then please refer to While Loop article here: Java While Loop.

### Factorial Program in Java using Functions

This Java program allows the user to enter any integer value. User entered value will be passed to the Method we created. Within this User defined function, this java factorial program will find Factorial of a given number using the For Loop

// Factorial Program in Java using Functions package FrequentPrograms; import java.util.Scanner; public class FactorialNumberUsingFunctions { private static Scanner sc; private static long Factorial = 1; public static void main(String[] args) { int Number; sc = new Scanner(System.in); System.out.println(" Please Enter any number to Find Factorial: "); Number = sc.nextInt(); Factorial = FactorialNumber(Number); System.out.format(" Factorial of %d = %d", Number, Factorial); } public static long FactorialNumber (int Number) { int i; for (i = 1; i <= Number; i++) { Factorial = Factorial * i; } return Factorial; } }

**OUTPUT**

**ANALYSIS**

In this java factorial program using functions example, We assigned the function return value to a long variable. Because the FactorialNumber(Number); function will return the long value as output.

Factorial = FactorialNumber(Number);

When the compiler reaches to FactorialNumber(Number) line in the main() program, the Jcompiler will immediately jump to below function:

public static long FactorialNumber (int Number) {

We already explained the LOGIC in the above Java factorial program example.

The last line ends with a *return Factorial* Statement. It means every time we call the FactorialNumber( ) function it will return factorial value of type long.

### Java Factorial Program using Recursion

This Java factorial program using Recursion allows the user to enter any integer value. User entered value will be passed to the Function we created. Within this User defined function, this program will find Factorial of a number Recursively.

In this Java program, we are dividing the code using the Object-Oriented Programming. To do this, first, we will create a class that holds a method to reverse an integer recursively.

package FrequentPrograms; public class FactorialNumber { public long Factorial_Number (int Number) { if (Number == 0 || Number == 1) { return 1; } else { return Number * Factorial_Number (Number -1); } } }

Within the Main Java factorial program, we will create an instance of the above-specified class and call the methods

package FrequentPrograms; import java.util.Scanner; public class FactorialNumberUsingRecursion { private static Scanner sc; public static void main(String[] args) { int Number; long Factorial = 1; sc = new Scanner(System.in); System.out.println(" Please Enter any number to Find Factorial: "); Number = sc.nextInt(); FactorialNumber fn = new FactorialNumber(); Factorial = fn.Factorial_Number(Number); System.out.format(" Factorial of %d = %d", Number, Factorial); } }

**OUTPUT**

**ANALYSIS**

**FactorialNumber Class Analysis:**

In this java factorial program using Recursion, Within this class, we defined a function. The following function will accept integer values as parameter value and return an integer value

public long Factorial_Number (int Number) {

Within the user-defined function, We used the If Else Statement to check whether the Given Number is Equal to 0 or Equal to 1.

- If the condition is TRUE, then the function will return 1.
- If the condition is False, then the function will return Number * (Number -1) recursively.

User Entered Value = 8

First If statement fails So,

Factorial = Number * Factorial_Number(Number -1);

= 8 * Factorial_Number (8 -1)

= 8 * Factorial_Number (7)

Factorial = 8 * 7 * Factorial_Number (6)

= 8 * 7 * 6 * Factorial_Number (5)

= 8 * 7 * 6 * 5 * Factorial_Number (4)

Factorial = 8 * 7 * 6 * 5 * 4 * Factorial_Number (3)

= 8 * 7 * 6 * 5 * 4 * 3 * Factorial_Number (2)

= 8 * 7 * 6 * 5 * 4 * 3 * 2 * Factorial_Number (1)

Factorial = 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1

= **40320**