Object rows and aliases

Objects extend the table with one row per object, referenced by name:

Counter c = new Counter();
Counter d = c;          // two names, ONE object
c.up(); c.up(); d.up();
System.out.println(c.get());   // 3
System.out.println(d.get());   // 3 — same object

| object | count | | ------ | ----- | | the one c and d share | 3 |

The three exam-favorite object questions, and how the table answers them:

1. Alias or copy? d = c copies the arrow, not the object. Both names mutate one row.
2. Order of calls. c.up() twice then d.up() once is 3; if the calls were interleaved differently the single shared row would show it. Objects do not remember who touched them.
3. State at print time. A getter returns the row's current value — so trace every mutation before any read, in order.

Worked FRQ-style trace:

public class Accum {
    private int total;
    public void add(int v) { if (v > 0) total += v; }
    public int get() { return total; }
}
Accum a = new Accum();
a.add(5); a.add(-2); a.add(3);

The object's row: total goes 0 → 5 → 5 → 8 (the negative add is filtered). Any question about a.get() is answered by reading that row at the right moment — including "what does a second Accum see?" (nothing: each object has its own row).