Factorial using Recursion in Java

Question

I am learning Java using the book Java: The Complete Reference. Currently I am working on the topic Recursion.

Please Note: There are similar questi

Answer 1

Your confusion, I believe, comes from the fact that you think there is only one result variable, whereas actually there is a result variable for each function call. Therefor, old results aren't replaced, but returned.

TO ELABORATE:

int fact(int n)
{
    int result;

   if(n==1)
     return 1;

   result = fact(n-1) * n;
   return result;
}

Assume a call to fact(2):

int result;
if ( n == 1 ) // false, go to next statement
result = fact(1) * 2; // calls fact(1):
|    
|fact(1)
|    int result;  //different variable
|    if ( n == 1 )  // true
|        return 1;  // this will return 1, i.e. call to fact(1) is 1
result = 1 * 2; // because fact(1) = 1
return 2;

Hope it's clearer now.

Answer 2

result is a local variable of the fact method. So each time the fact method is called, the result is stored in a different variable than the previous fact invocation.

So when fact is invoked with 3 as argument, you can imagine that its result is

 result3 = fact(2) * 3
 result3 = result2 * 3
 result3 = 1 * 2 * 3

Answer 3

What happens is that the recursive call itself results in further recursive behaviour. If you were to write it out you get:

 fact(4)
 fact(3) * 4;
 (fact(2) * 3) * 4;
 ((fact(1) * 2) * 3) * 4;
 ((1 * 2) * 3) * 4;

Answer 4

public class Factorial {
public static void main(String[] args) {
   int n = 7;
   int result = 1;
   for (int i = 1; i <= n; i++) {
       result = result * i;
   }
   System.out.println("The factorial of 7 is " + result);
}
}

Answer 5

A recursive solution using ternary operators.

public static int fac(int n) {
    return (n < 1) ? 1 : n*fac(n-1);
}

Answer 6

The correct one is :

int factorial(int n)
{
    if(n==0||n==1)
        return 1;
    else 
        return n*factorial(n-1);
}

This would return 1 for factorial 0. Do it believe me . I have learned this the hard way. Just for not keeping the condition for 0 could not clear an interview.