import tester.*;
  
// to represent a book and its author
class Book{
  String title;
  Author author;
  
  // Constructor for a book that 
  // notifies the author that his book has been published
  Book(String title, Author author){
    this.title = title;
    this.author = author;
    this.author.addBook(this);
  }

  /* TEMPLATE
  ... this.title ...   -- String 
  ... this.author ...  -- Author
	 
  METHODS:
  ... this.sameBook(Book) ...             -- boolean
	 
  METHODS FOR FIELDS:
  ... this.author.addBook(Book) ,,,       -- void
  ... this.author.sameAuthor(Author) ...  -- boolean
  */
  
  // is this book the same as the given book?
  boolean sameBook(Book that){
    return
    this.title.equals(that.title) &&
    // here we only check the author's name to break the circularity
    this.author.name.equals(that.author.name);
  }
}
  
// to represent an author of a book
class Author{
  String name;
  Book book;
    
  // Constructor for the author who has yet to write a book
  Author(String name){
    this.name = name;
  }

  /* TEMPLATE
  ... this.name ...   -- String 
  ... this.book ...   -- Book
  
  METHODS:
  ... this.sameAuthor(Author) ...             -- boolean
	   
  METHODS FOR FIELDS:
  ... this.book.sameBook(Book) ...  -- boolean
  */
    
  // EFFECT:
  // make the given book this author's book
  void addBook(Book book){
    this.book = book;
  }
    
  // is this author the same as the given author?
  boolean sameAuthor(Author that){
    return
    this.name.equals(that.name) &&
    this.book.sameBook(that.book);
  }
}
  
// Examples for circularly referential books and authors
class ExamplesBook{
  ExamplesBook(){}

  // three authors
  Author mf = new Author("MF");
  Author mf2 = new Author("MF");
  Author ebw = new Author2("EBW");
  
  // and the three book they wrote
  Book htdp = new Book("HtDP", this.mf);
  Book htdp2 = new Book("HtDP", this.mf2);
  Book eos = new Book("EOS", this.ebw);
  
  // test the method sameBook and some properties of the Book/Author data
  void testSameBook(Tester t){

    t.checkExpect(this.htdp.author.name, "MF");
    t.checkExpect(this.htdp.title, "HtDP");
    t.checkExpect(this.eos.author.name, "EBW");
    t.checkExpect(this.htdp.sameBook(this.htdp2), true);
  }
}