Answers to Self-Study Questions

Test Yourself #1

public Stack() {
  items = new Object[INITSIZE];
  numItems = 0;
}

Test Yourself #2

public Object pop() throws EmptyStackException {
  if (numItems == 0) throw new EmptyStackException();
  else {
    numItems--;
    return items[numItems];
  }
}

Test Yourself #3

Test Yourself #4

public void push(Object ob) {
  items = new Listnode(ob, items);
  numItems++;
}

Test Yourself #5

Test Yourself #6

public static void reverseQ(Queue q) {
  // precondition: q contains x1 x2 ... xN (with x1 at the front)
  // postcondition: q contains xN ... x2 X1 (with xN at the front)
  Stack s = new Stack();
  while (!q.empty()) s.push(q.dequeue());
  while (!s.empty()) q.enqueue(s.pop());
}