/**
 * A Stack is an object that holds a collection of
 * Strings.
 */
public class Stack implements Worklist {
  private Node top = null; // The top Node in the stack
  /**
   * Push a String on top of this stack.
   * @param data the String to add
   */
  public void add(String data) {
    top = new Node(data,top);
  }
  /**
   * Test whether this stack has more elements.
   * @return true if this stack is not empty
   */
  public boolean hasMore() {
    return (top != null);
  }
  /**
   * Pop the top String from this stack and return it.
   * This should be called only if the stack is
   * not empty.
   * @return the popped String
   */
  public String remove() {
    Node n = top;
    top = n.getLink();
    return n.getData();
  }
}