import java.util.*;

/**
 * <p> <code>class Stack</code> is a <b>simple</b> implementation of a
 * <i>stack</i> data structure.  Basic operations are:  pop, push,
 * and top.  The stack is implemented using a <code>Vector</code>. </p>
 *
 * @author G.D.Thurman
 * @version 99.09.24
 * @see Vector
 */

public class Stack implements Csxxx_Containers {

   private Vector elems;

   public Stack() { this(DFLT_NELEMENTS); }
   public Stack(int len) { elems = new Vector(len); }

   public boolean push(Object elem)  { 
		boolean rv;
		if (elems.size() == elems.capacity())
			rv = false;
		else {
			elems.addElement(elem); 
			rv = true;
		}
		return rv;
	}
   public Object pop() {
		Object rv;
		int size = elems.size();
		if (size == 0) 
			rv = null;
      else {
			rv = top();
			elems.removeElementAt(size - 1);
		}
      return rv;
   }
   public Object top() {   
      return elems.size() <= 0 ? null : elems.elementAt(elems.size()-1);
   }

   public int size() { return elems.size(); }
   public int capacity() { return elems.capacity(); }
   public void clear() { elems.removeAllElements(); }
   public boolean isEmpty() { return elems.size() == 0; }
   public boolean isFull() { return elems.size() == elems.capacity(); }
   public String toString() {
      int size = elems.size();
      String s = new String("stack contents:" + "\n" +
                            "===============\n");
      for (int i = size-1; i >= 0; i--)
         s += "\t" + elems.elementAt(i) + "\n"; 
      s += "size: " + elems.size() + "; capacity: " + elems.capacity();
      return s;
   }

   public static void main(String[] argv) {
      Stack s = new Stack();
      for (int i = 0; i < argv.length && s.push(argv[i]); i++) 
			; 
      System.out.println(s);
      if (!s.isEmpty()) {
         System.out.println("\npop: " + s.pop());
         System.out.println("top: " + s.top());
         System.out.println("size: " + s.size());
         System.out.println("capacity: " + s.capacity());
      }
      s.clear();
      System.out.println("\n*** stack cleared\n\n" + s);
		//s.pop();
   }
}