Java-递归

Question

The following is my adaptation of an AP Computer Science question. The book says it should print 00100123 I think it should print 0010012 But the code below actually prints 3132123

What is going on? Also it does not appear to have any stop condition?!

public class Mystery {

    public static void main(String[] args) {
        int n;
        n = 3;
        mystery(n);
    }

    public static void mystery(int n) {
        int k;
        for (k = 0; k < n; k++) {
            mystery(k);
            System.out.print(n);
        }
    }
}

The actual question reads: Consider the following method.

public void mystery (int n)
{
     int k;
     for (k=0 ; k < n ; k++)
     {
          mystery(k);
          System.out.print(n);
     }
}

What value is returned by the call mystery (3)?

I now understand that the loop forms the stop condition and I think I understand jhamon's comment "last instruction is to print n. n is 3, there is no way it prints only '0010012'" but I don't understand why the book says it should print 00100123.

As Batsheba says I have tried watching the variables while debugging but the book says it should print 00100123. Thanks very much jhamon for the corrected code , so from what I can see the book is wrong?

Answer 1

That program cannot print "0". It prints n , and if n is 0 it will never reach the System.out.print(n) line. That line is inside the for statment with k<n .

As others have pointed out in the comments, that condition in the for loop is also the stop condition. mystery will recursively call itself n times. However, in each of these calls, the parameter is smaller.
(For fun, try changing the condition to k <= n . Then it will not terminate, because the parameter is smaller or equal ).

If you change the line to print(k) , which is what was probably intended, it will indeed print "0010012". Here is an ideone link to show that.