# find factorial number in java

## Java Program to Find the Factorial of a Number

Factorial of a non-negative integer, is multiplication of all integers smaller than or equal to n. For example factorial of 6 is 6*5*4*3*2*1 which is 720.

Below questions may asked by interviewer

Q) So, basically what is factorial?

Ans: A factorial is a function that multiplies number by every number. For example 4!= 4*3*2*1=24. The function is used, among other things, to find the number of ways “n” objects can be arranged.

Q) How to calculate?

For example :

Consider :

• 2! = 2 x 1 = 2

The possibility of 2! is two ways like {2,1}, { 1,2 }.

Same as like :

4! = 4 x 3 x 2 x 1 = 24.

• 24 = the arrangement of 4! is {1,2,3,4}, {2,1,3,4}, {2,3,1,4}, {2,3,4,1}, {1,3,2,4}, etc.

Same as like 5! , 10! , N!.

The following program has been written in 5 different ways, using while loop, for loop, do while loop, using method.

Now, let’s get into the programming part.

1. Java Program To Calculate Factorial using standard values with outputs

Method 1
```/*
* Author: Zameer Ali
* */
class Factoral {
public static void main(String arg[]) {
int n = 5, fact = 1;

for (int i = 1; i <= n; i++) {
fact = fact * i;
}

System.out.println("factoral=" + fact);
}
}
```

Output:

factorial =120

2. Find Factorial Using For Loop getting user input

Method 2
```/*
* Author: Zameer Ali
* */
import java.util.Scanner;
class Factorial {
public static void main(String arg[])
{

long n, fact = 1;

Scanner sc = new Scanner(System.in);

System.out.println("enter number");

n = sc.nextLong();

for (int i = 1; i <= n; i++) {

fact = fact * i;

}

System.out.println("fact=" + fact);

}
}
```

Output:

enter number
7=5040

3. Find Factorial using Function

Method 3
```/*
* Author: Zameer Ali
* */
import java.util.Scanner;
class Factorl {
public static void main(String args[])

{

long n, fact = 0;

n = Long.parseLong(args);

fact = factCal(n);

System.out.println("fact=" + fact);

}

static long factCal(long x) {
long fact = 1;
for (int i = 1; i <= x; i++) {

fact = fact * i;

}
return fact;
}

}
```

Output:

C:\Users\ZameerAli\Desktop\E>javac.java

C:\Users\ZameerAli\Desktop\E>java Factorl 10

factorl=3628800

4. Find Factorial Using Recursion

Recursion: A Recursion is a function call itself – you can check out more information about what is recursion in java here?

Method 4
```/*
* Author: Zameer Ali
* */
import java.util.Scanner;
class Factorl {
public static void main(String arg[]) {
long n;

Scanner sc = new Scanner(System.in);

System.out.println("enter number");

n = sc.nextLong();

long f = Factorl.fact(n);

System.out.println("factorial=" + f);
}

static long fact(long n) {
if (n <= 0)
return 1;

return Factorl.fact(n - 1) * n;
}

}
```

Output:

enter number
30
Factorl=8764578968847253504

5. Find Factorial Using while loop and do while loop

Method 5
```/*
* Author: Zameer Ali
* */
import java.util.Scanner;

class Factrl {
public static void main(String arg[])

{

long n, fact = 1;

Scanner sc = new Scanner(System.in);

System.out.println("enter number");

n = sc.nextLong();
int i = 1;
while (i <= n) {

fact = fact * i;
i++;
}

System.out.println("fact=" + fact);

}

}
```

Output:

enter number
10
fact=3628800

Do while loop example

Method 6
```/*
* Author: Zameer Ali
* */
import java.util.Scanner;

class Fact1 {
public static void main(String arg[])

{

long n, fact = 1;

Scanner sc = new Scanner(System.in);

System.out.println("enter number");

n = sc.nextLong();

int i = 1;

do {
fact = fact * i;
i++;
}
while (i <= n);

System.out.println("fact=" + fact);

}

}
```

Output:

output:
enter number
7
fact=5040