**How to find factorial of a number in Java**on both recursive and iterative way is a common Java interview question mostly asked at fresher level. It’s not just popular on Java interview but also on other programming language like C or C++. Its also famous In our last article we have seen how to check if a number is prime or not and in this Java programming tutorial we will see a simple

**Java program to find factorial of a number in Java**by using

**recursion**and iteration. Same program can also be used to

*print factorial of any number*or printing a range of factorial as well. Let’s talk about logic, factorial of a number is calculated by formula number*(number -1) till zero and since

**value of factorial zero is 1**, it acts as a

**base case in recursive version of factorial method**. logic to find factorial of number is encapsulated inside factorial(int number) and fact(int number) method.

This Java programming tutorial is in next with my earlier tutorial for beginners like Java Program to reverse String in Java with recursion , Java program to free memory in java and recently how to read and write on text file in Java etc, if you haven’t read them you may find them interesting and useful.

__How to find factorial of number in Java using recursion and iteration__:

In this section we will see complete

**code example of Java program to calculate factorial of a number**in both recursive and iterative way. If you look at closely you will find that recursive solution of calculating factorial is much easier to write and pretty intuitive to read as it represent formula number*(number -1). Any way recursion should only be limited for educational purpose as it is always subject to**stack overflow error**if recursion is too deep. Calculating factorial of a number is also a good programming question to exercise for anyone who is just started learning programming. Anyway here is example of Java program to find factorial of a number :

*/***

* Simple Java program to find factorial of a number using recursion and iteration.

* Iteration will use for loop while recursion will call method itself

*/* Simple Java program to find factorial of a number using recursion and iteration.

* Iteration will use for loop while recursion will call method itself

*/

**public**

**class**FactorialInJava{

**public**

**static**

**void**main(

**String**args[]) {

*//finding factorial of a number in Java using recursion - Example*

**System**.out.println("factorial of 5 using recursion in Java is: " + factorial(5));

*//finding factorial of a number in Java using Iteration - Example*

**System**.out.println("factorial of 6 using iteration in Java is: " + fact(6));

}

*/**

* Java program example to find factorial of a number using recursion

* @return factorial of number

*/

* Java program example to find factorial of a number using recursion

* @return factorial of number

*/

**public**

**static**

**int**factorial(

**int**number){

*//base case*

if(number == 0){

**return**1;

}

**return**number*factorial(number -1);

*//is this tail-recursion?*

}

*/**

* Java program example to calculate factorial using while loop or iteration

* @return factorial of number

*/

* Java program example to calculate factorial using while loop or iteration

* @return factorial of number

*/

**public**

**static**

**int**fact(

**int**number){

**int**result = 1;

while(number != 0){

result = result*number;

number--;

}

**return**result;

}

}

**Output:**

factorial of 5 using

**recursion**in Java is: 120

factorial of 6 using

**iteration**in Java is: 720

That's all on

**how to calculate or find factorial of number in Java**. Both iterative and*recursive version of factorial*can be used to calculate factorials but beware of StackOverFlowError if a larger number is passed to recursive version of factorial method in Java.
## 12 comments :

Just for the sake of completeness (which you undoubtedly know):

/**

* Tail recursive factorial.

*/

public static long factail(int number, long result) throws Exception {

if (number == 0) {

throw new Exception("result: " + result);

}

return factail(number - 1, result * number);

}

Of course, JVMs do not (like functional language interpreters or compilers) usually optimize for tail recursion, as the stack trace shows.

Sorry, forgot to add in the last post that you should call the auxiliary with result = 1.

public static long factorial(int number) throws Exception {

return factail(number, 1);

}

private static long factail(int number, long result) throws Exception {

if (number == 0) {

throw new Exception("result: " + result);

}

return factail(number - 1, result * number);

}

Indeed writing program to calculate factorial is good example for learning recursion. by the way is it tail recursive ?

At what point does this break down, because I've tested both methods incrementally up to 16 and they both give the same result (2004189184), but if you use 17 as the number then what you get back is a negative result, which cannot be correct (-288522240).

Why does this happen?

I think factorial program is not the best to understand recursion. The best way to understand recursion is to call a function twice i.e.

recursive()

{

System.out.println("Hello");

}

calling()

{

recursive();

recursive();

}

If you understand this then you probably know how recursion works.

I'd do it like this...

public static Integer factorial(int number) {

if (number == 1) {

System.out.println("Factorial ended");

return 1;

} else {

return number*factorial(number-1);

}

}

Could you write a program to calculate factorial but condition being you call the recursive function within a for loop

I do want to point out the question above regarding the negative result when retrieving the factorial for 17. This is because the primitive int is being used. To get around this then it is advised to use the BigInteger Object type.

What kind of cache did you mean, when said this:

Since factorial of a number is equal to number multiplied by factorial of previous number, you can cache those value instead of recalculating them, this will impress your interviewer a bit. See the solution for full code example.

Read more: http://java67.blogspot.com/2015/03/top-40-core-java-interview-questions-answers-telephonic-round.html#ixzz3zUhrpWh9

Hi, I mean you can cache factorials instead of calculating again e.g. factorial(6) = 6* factorial(5), instead of calculating factorial(5), you can replace with 120. You can use any cache e.g. in memory, disk base or cloud based, upto you. simplest is a in memory HashMap cache.

IMHO, it happens implicitly, isn't it?

Sorry, didn't get you. If you don't store already calculated value they will be lost, you need to memoization technique, which is also popular in calculating fibonacci series.

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