/**
  * Implement the Stack interface from the textbook
  * by wrapping the standard class java.util.Stack.
  * 
  * @author Yuan Chen
  */
 
  
public class JavaStack implements Stack {
 
  /** Implement via java.util.Stack.  We only need to rename some
   * methods, throw some exceptions that java.util.Stack tolerates
   * silently, and keep track of the stack size.
   */
  java.util.Stack s;

  /** Size of the stack. */
  private int size;
 
  // We don't need many Javadoc comments here, because the behavior of
  // these methods is already documented in the Stack interface, which
  // we implement.  Anything special about the implementation (e.g.,
  // runtime) could be documented here.
  
  public JavaStack() {
    s = new java.util.Stack();
    size = 0;   // not strictly necessary
  }

  public int size() {
    return size;
  }
 
  public boolean isEmpty() {
    return s.empty();
  }
 
  public Object top() {
    if (isEmpty())
      throw new StackEmptyException("Stack is empty.");
    return s.peek();  
  }
    
  public void push (Object element) {
    s.push(element);  // never have to throw StackFullException
    size++;
  } 

  public Object pop() {
    // fill this in
    return null;  // replace this!
  } 
}