Question

why do i get this output ? I expect the output to be 10,9,8…

But it is 11,12,13….

class tester {

    static int i = 0;

    public static void main(String args[]) {
        recursive();
        System.out.println("after recursive");
    }

    public static void recursive() {
        while(i++<10) {
            recursive();
            System.out.println(i);
        }
    }

}

Answer 1

The simple logic is as follows:

Since your incremental is a posfix increment, the original value is evaluated first, before increment.

Logic:

while (i++ < 10) { recursive();}

1. i is initially 0, so, 0 < 10 (true), increment by 1. Now, call recursive().

This loops (1) until i = 10. When i = 10 is evaluated, the while expression is false, so it leaves the loop.

Remember, we have already called recursive() 10 times already, so it now needs to print i, 10 times, (since the JVM pushed recursive() function 10 times in the stack). Each times it pops the function, it goes back to the System.out.println(i) statement, knowing that i was incremented in each call, hence why you see values:

11
12
13
14
15
16
17
18
19
20
after recursive

That’s basically recursion in a nutshell. 🙂