A library maintains books on various subjects.

Part 1. (4 points) For each Book object, the information of interest is:

• the title (a string);
• the authors (a string);
• the publisher (a string);
• the publication year (an integer).

• creation of a Book, given its title, authors, publisher, and publication year;
• getTitle: that returns the title of the book;
• getAuthors: that returns the authors of the book;
• getPublisher: that returns the publisher of the book;
• getYear: that returns the publication year of the book.

Part 2. (16 points) For each topic (identified by its name, a string), the books on that topic available in the library shop are stored in a BookList data structure. Each book in a BookList is assigned a progressive number (an integer), starting from 0.

Realize a Java class BookList, to represent BookList objects, that exports the following functionalities:

• creation of a BookList, given the topic; the created BookList is initially empty (i.e., it contains no books);
• getTopic: that returns the topic;
• addBook: that, given a Book object, inserts it into the book list, assigning it the next available progressive number (i.e., one plus the number of the last book in book list);
• getBook: that, given an integer n, returns the book object with progressive number n in the book list; if n does not correspond to a number of a book in the list (i.e., n is either negative or greater or equal than the number of books in the list), then an exception is thrown;
• findBook: that, given the title t of a book, returns the progressive number of the first book object with title t in the book list, if such an object is present in the book list, and -1 otherwise;
• removeBook: that, given an integer n, removes from the book list the book object with progressive number n, if n corresponds to a number of a book in the list, throws an exception otherwise; note that, when a book is removed from the book list, the progressive number assigned to each subsequent book in the book list is decreased by 1;
• numBooks: that returns the number of books in the book list;
• booksByAuthor: that, given a string s (representing the name of an author), returns an array of integers containing the progressive numbers of all books in the book list for which s appears among the authors (i.e., s is a substring of the string representing the authors of the book).

  Hint: use the method int indexOf(String s) of the String class, which returns the index within this string of the first occurrence of s, if s is a substring of this string, and -1 otherwise.

Part 3. (6 points) Realize a static method writeBooksByAuthor, client of the class BookList (i.e., external to such a class) that, given a BookList object bl, a string s (representing the name of an author), and the name f of a file, writes on the file f the title and authors of all those books in bl for which s appears among the authors, one book per line. The method should catch exceptions due to input/output errors that may occur, and print suitable error messages.

Part 4. (4 points) Discuss the notion of parameter passing in Java. Illustrate the difference between passing parameters of type (reference to an) object and of primitive types. Provide an example in which this difference becomes evident.