/**
 * Book models the behaviour of a book
 */
class Book {
  
  // instance variables
  private int numCopies;
  
  /**
   * sign out a copy of this book
   */
  public void checkOut() {
  }
  
  /**
   * buy copies for the collection
   * @param copies The number of total copies purchased
   */
  public void buyCopies(int copies) {
  }
  
  /**
   * bring a copy back to the library
   */
  public void checkIn(){
  }
  
  /**
   * get the number of copies available at this time
   * @return numCopies
   */
  public int getNumCopies() {
    return numCopies;
  }
}