// Textbook fragment 06.03
/** Realization of an indexed list by means of an array, which is doubled
  * when the size of the indexed list exceeds the capacity of the array.
  */
public class ArrayIndexList<E> implements IndexList<E> {
  private E[] A;              // array storing the elements of the indexed list
  private int capacity = 16;  // initial length of array A
  private int size = 0;       // number of elements stored in the indexed list
  /** Creates the indexed list with initial capacity 16. */
  public ArrayIndexList() {
    A = (E[]) new Object[capacity]; // the compiler may warn, but this is ok
  }
  /** Inserts an element at the given index. */
  public void add(int r, E e)
    throws IndexOutOfBoundsException {
    checkIndex(r, size() + 1);
    if (size == capacity) {             // an overflow
      capacity *= 2;
      E[] B =(E[]) new Object[capacity];
      for (int i=0; i<size; i++)
        B[i] = A[i];
      A = B;
    }
    for (int i=size-1; i>=r; i--)       // shift elements up
      A[i+1] = A[i];
    A[r] = e;
    size++;
  }
  /** Removes the element stored at the given index. */
  public E remove(int r)
    throws IndexOutOfBoundsException {
    checkIndex(r, size());
    E temp = A[r];
    for (int i=r; i<size-1; i++)        // shift elements down
      A[i] = A[i+1];
    size--;
    return temp;
  }