/**
 * This class implements a peekable generic Stack as a dynamic array;
 * a peekable stack allows the user to access any stack element.
 */
public class PeekableStack<T> extends Stack<T> {

  /* Note that there's no <T> in the constructor definition */
  PeekableStack(int initialSize) {
    super(initialSize);
  }

  /**
   * Peeks at the kth element, where the bottom of the stack has
   * position 1, and increases as we go up to the stack top.
   */
  public T peek(int k) {
    if (k < 1 || size < k)
      throw new RuntimeException("Trying to peek at a nonexistent element.");
    return istack[size-k];
  }
}