final sclass SimpleStack<A> extends RandomAccessAbstractList<A> {

  new ArrayList<A> l;

  int peak;

  public A get(int i) { ret l.get(i); }

  public int size() { ret l.size(); }

  public A set(int i, A a) { ret l.set(i, a); }

  public void add(int i, A a) { l.add(i, a); checkSize(); }

  public A remove(int i) { A a = l.remove(i); checkSize(); ret a; }

  void checkSize {

    int n = size();

    if (n > peak) peak = n; // record new peak size (~actual capacity)

    if (n*2 < peak) { // shrink physically when below half of peak

      ifdef SimpleStack_debug

        print("Shrinking SimpleStack: " + peak + " => " + n);

      endifdef

      trimToSize(l);

      peak = n;

    }

  }

}