public class ArrayStack implements Stack {
  public int capacity;
  public Object []array;
  public int size;
  
  public ArrayStack() {
    this(256);
  }
  
  public ArrayStack(int capacity) {
    array = new Object[capacity];
    this.capacity = capacity;
    size = 0;
  }
  
  public int size() {
    return size;
  }
  
  public void push(Object o) {
  
    if( size >= capacity-1 ) {
      capacity *= 2;
      Object []newArray = new Object[capacity];
      for(int i=0; i<array.length; i++)
        newArray[i] = array[i];
      array = newArray;
      newArray = null;
    }
    array[size++] = o;
  }
  
  public Object pop() {
    return array[--size];
  }
  
  public Object top() {
    return array[size-1];
  }
  
  public String toString() {
    String str = "@@@@@@@@ - Stack - @@@@@@@@\n";
    for(int i=size-1; i>=0; i--)
      str += array[i].toString()+"\n";
    return str + "@@@@@@@@@@@@@@@@@@@@@@@@@@@\n";
  }  
}