CODEWITHSUNDEEP
javarecursion
Harry
Harry

Reputation: 163

Basic recursion with if else statement (java)

Reviewing my notes and was wondering if anyone has a concise explanation for what is occurring below:

public class HelloWorld{

public static void main(String[]args){
    helloWorld(10);

}

public static void helloWorld(int n){
      if(n > 0){
        System.out.println("HelloWorld! " + n);
        helloWorld(n-1);
        }
        System.out.println("GoodBye from " + n);
      }
    }

Output: 

HelloWorld! 10
HelloWorld! 9
HelloWorld! 8
HelloWorld! 7
HelloWorld! 6
HelloWorld! 5
HelloWorld! 4
HelloWorld! 3
HelloWorld! 2
HelloWorld! 1
GoodBye from 0
GoodBye from 1
GoodBye from 2
GoodBye from 3
GoodBye from 4
GoodBye from 5
GoodBye from 6
GoodBye from 7
GoodBye from 8
GoodBye from 9
GoodBye from 10

Just to be clear, I totally understand what's happening above with the recursion and the call stack unwinding. My question is about what happens when I include an else statement below: 

public static void helloWorld(int n){

    if(n > 0){
        System.out.println("HelloWorld! " + n);
        helloWorld(n-1);

        }else{
        System.out.println("GoodBye from " + n);

        }
    }

Output: 

HelloWorld! 10
HelloWorld! 9
HelloWorld! 8
HelloWorld! 7
HelloWorld! 6
HelloWorld! 5
HelloWorld! 4
HelloWorld! 3
HelloWorld! 2
HelloWorld! 1
GoodBye from 0

Why does the call stack appear to not unwind when it hits the else statement?

Upvotes: 0

Views: 237

Answers (2)

kk.
kk.

Reputation: 3945

In 2nd case the else block will be executed only for n = 0 as it is going in the if block. However in the first case, after each recursion completes System.out.println("GoodBye from " + n); will be executed as it is not bound with any condition.

Upvotes: 1

Eran
Eran

Reputation: 393811

The call stack unwinds in both cases. It just doesn't print anything when it unwinds in the second snippet, since you only print "GoodBye from " + n when n is 0, which happens exactly once.

Upvotes: 4

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