Reading their recursion

The "what does this print" genre, decoded:

public static void puzzle(int n) {
    if (n <= 0) {
        return;
    }
    System.out.print(n + " ");
    puzzle(n - 2);
    System.out.print(n + " ");
}

puzzle(5) prints 5 3 1 3 5 — before the call for the descent, after it for the unwind. Number of prints: 2 per call that survives the base check (3 calls → 6 prints).

Mental rules:

• Code before the recursive call runs top-down (descent order).
• Code after the recursive call runs bottom-up (unwind order).
• Total calls = every invocation including base-case hits.
• Missing base case or a branch that can't reach it → StackOverflowError, never "runs forever" visibly.

Also know: recursion can always be replaced by a loop, but the exam wants you to read their recursion, not rewrite it.