Dart
Library class
Set up collection management with the Library class.
Library class and addBook
Now let's write the Library class that stores books. It has a List<Book> field and an addBook method. Each added book grows the list.
Example: class Library { List<Book> books = []; void addBook(Book b) { books.add(b); } }. Here books starts as an empty list. The addBook method takes a Book and appends it.
With this design you can add as many books as you want. The next lessons add checkout and search methods.
Initializing List<Book>
The line List<Book> books = []; creates an empty Book list. In Dart [] means an empty list. Because the type is Book, only Book objects can be added.
This gives type safety: books.add('text') is a compile error because 'text' is not a Book. Only books.add(Book(...)) is valid.
Read the list length with books.length. It tells you how many books are stored.
Exercise Add the Library class and addBook
The Book class is already defined. Now define a Library class with a List<Book> books = [] field and a void addBook(Book b) method. Inside the method write books.add(b). In main create a Library, add two books and print lib.books.length.
Show example solution
class Book {
String title;
bool borrowed = false;
Book(this.title);
}
class Library {
List<Book> books = [];
void addBook(Book b) {
books.add(b);
}
}
void main() {
var lib = Library();
lib.addBook(Book('Les Miserables'));
lib.addBook(Book('Crime and Punishment'));
print(lib.books.length);
}
Test yourself
-
What does the addBook method do?
void addBook(Book b) {
books.add(b);
}
- Removes the book
- Appends the book to the list
- Prints the book
- Lends the book out
Show answer
Appends the book to the list — addBook appends the given book to the list.
-
The books.add call
class Library {
List<Book> books = [];
void addBook(Book b) {
____.add(b);
}
}
Show answer
class Library {
List<Book> books = [];
void addBook(Book b) {
books.add(b);
}
}
-
Match the Library parts
- List<Book>
- Book list type
- books = []
- Empty start
- addBook(Book b)
- Add method
- books.add(b)
- Append to list
Next lesson: Checking out
