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 questions on stackoverflow. I searched them but I didn’t find the solution to my question. I am confused with the logic in the following program.

If I run the below program, it produces the correct output, but I didn’t understand the logic.

• I didn’t understand the logic in the following line : result = fact(n-1) * n;
• From my knowledge, If we pass the value of n=4 as shown in the below program,
• Then, 3 * 4 is stored in the result i.e., 12.
• Again, fact(n-1) is called. Then n becomes 3.
• Then the 2 * 3 is stored in the result replacing the previous 12.

• I think you understood where I am stuck up/confused.

• Thank you.

class Calculation
{
    int fact(int n)
    {
        int result;

       if(n==1)
         return 1;

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

public class Factorial
{
     public static void main(String args[])
     {
       Calculation obj_one = new Calculation();

       int a = obj_one.fact(4);
       System.out.println("The factorial of the number is : " + a);
     }
}

Answer 1

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