Mirror a stack of Integers
Overall this code looks decent. Just a few concerns:


For this kind of complex set of steps, it is always a good idea to add comments which will help the reader to understand the code
You can use the diamond operator here:

Queue&lt;Integer&gt; q = new LinkedList&lt;&gt;();

I might be opinionated, but I prefer the name val (or even v) rather than valq.

for (int i = 0; i &lt; size; i++) {
    int val = q.poll();
    s.push(val);
    q.offer(val);
}