Trace the Code Output

What they ask

The first stage for associate and junior engineers is an online IQ plus technical assessment (TestGorilla). Besides multiple choice items, there is a debugging-style task: a long, deliberately messy piece of code, and you write exactly what it prints when executed. No compiler, just you and the snippet.

A short example in the same spirit (the real one is longer and uglier):

class A {
    static int n = 0;
    int id;
    A() { id = ++n; System.out.print("A" + id + " "); }
    void hi() { System.out.print("hiA "); }
}
class B extends A {
    B() { super(); System.out.print("B" + id + " "); }
    @Override void hi() { System.out.print("hiB "); }
}
public class Main {
    static void touch(A a) { a.id = 99; a = new A(); }
    public static void main(String[] args) {
        A x = new B();
        x.hi();
        touch(x);
        System.out.print(x.id + " ");
        Integer p = 127, q = 127, r = 128, s = 128;
        System.out.print((p == q) + " " + (r == s));
    }
}

What they look for

• Constructor chaining order (parent runs first), static counters shared across instances, dynamic dispatch on hi().
• Java passes references by value: touch mutates the shared object but its reassignment is invisible to the caller.
• Small language traps like the Integer cache (127 boxed values compare equal with ==, 128 do not).
• Discipline: writing intermediate values in the margin instead of guessing the final line.

Expected output of the example: A1 B1 hiB A2 99 true false.