Storing an object within an object

Question

Since my post yesterday regarding constructing a link list from scratch I have made some progress.

I have encountered a new hurdle: storing an object within an object.

Lets say I have a 'book' class with the following attributes (forgetting all the set & get methods which I am familiar with):

 private String title;
 private int rating;

How would I then reference another class such as 'author' as obviously a book must have an author and many books may have the same or more then one author.

Here is my 'author' class attributes (again ignoring gets & sets):

 String authorName;
 String authorEmail;

Am I right in thinking I need to initiate an object of 'author' within the 'book' class as such:

 private String title;
 private int rating; //mine
 private Author author = new Author();

Would I then have to set the attributes authorName and authorEmail everytime I made a new instance of 'book'?

Many thanks in advance for constructive feedback.

Answer 1

You don't necessarily need to instantiate the Author object right there where you declare the attribute. I would suggest something like passing in an already-instantiated Author either to the constructor of the Book class or to a setter. Then you could pass the same Author in to each Book you create that should be associated with it.

EDIT: added some code snippets:

For instance, if you made your Book constructor something like this:

public Book(String title, int rating, Author author) {
    // set this.title, this.rating, and this.author to the passed-in parameters...
}

Then you would invoke it in code like this:

Author bob = new Author(); 
// You can set the name and email of the Author here using setters,
//   or add them as args in the Author constructor
Book firstBook = new Book("The First Book", 1, bob);
Book secondBook = new Book("The Second Book", 2, bob);