I am learning Java from a book, and come across a chapter regarding recursion using a factorial example.
//A simple example of recursion
package tutorials;
class Factorial {
// this is a recursive method
int fact (int n) {
int result;
if(n==1) return 1;
result = fact(n - 1) * n;
return result;
}
}
class Recursion {
public static void main(String args[]) {
Factorial f = new Factorial();
System.out.println("Factorial of 3 is " + f.fact(3));
System.out.println("Factorial of 4 is " + f.fact(4));
System.out.println("Factorial of 5 is " + f.fact(5));
}
}
The result this piece of code gives is "Factorial of 3 is 6" and "Factorial of 4 is 24"
What i don't understand is what is happening in the class Factorial and why *n is not calculated immediately. The book does not do a very good job of explaining this so i thought i would ask any experienced programmers for help.
If you invoke fact(5), here is how it will work:
fact(5)
5*fact(4)
4*fact(3)
3*fact(2)
2*fact(1)
2*1=2 //(since if n==1, 1 is returned directly
result=2
result=3*2
result=4*3*2
result=5*4*3*2
result=120
Recursion simply means you invoke a method within itself, usually after manipulating the argument to suit your end result (n - 1 in this case). You also make sure you define a terminal condition (n==1 in this case). Internally, the variables are pushed on to a stack to be remembered for every invocation, but that's probably a discussion for another day