/**
  * Copyright (c): Uwe Schmidt, FH Wedel
  *
  * You may study, modify and distribute this source code
  * FOR NON-COMMERCIAL PURPOSES ONLY.
  * This copyright message has to remain unchanged.
  *
  * Note that this document is provided 'as is',
  * WITHOUT WARRANTY of any kind either expressed or implied.
  */

/**
 *
 * @author Uwe Schmidt
 *
 * ein einfacher stack
 * der das interface implementiert
 *
 * Implementierung aus der SimpleStack Klasse
 * uebernommen
 */

//--------------------

public
class Stack1
implements StackInterface {

  //--------------------

  // die Datenfelder fuer die Implementierung

  private
  Object[] elems;

  private
  int top;

  //--------------------

  // die Konstruktoren

  public
  Stack1(int max) {
    elems = new Object[max];
    top = 0;
  }

  public
  Stack1() {
    this(20);
  }

  //--------------------

  // alle Funktionsruempfe

  //--------------------

  public
  boolean isEmpty() {
    return
      top == 0;
  }

  //--------------------

  public
  Object top()
  {
    assert top > 0 : "Stack1.top: empty stack" ;

    return
      elems[top - 1];
  }

  //--------------------

  public
  void push(Object o) {
    elems[top++] = o;
  }

  //--------------------

  public
  void pop()
  {
    assert top > 0 : "Stack1.pop: empty stack";

    elems[--top] = null;
  }

  //--------------------
  //
  // auch die Vorbedingungen muessen implementiert werden
  // Gefahr: Codeverdopplung

  public
  boolean prePop() {
    return
      ! isEmpty();
  }

  public
  boolean preTop() {
    return
      ! isEmpty();
  }

}

//--------------------