Checking out
- Dart course
- Intermediate
- Lesson 55/116
- 6 min
Write the checkout flow with checkout and return methods.
checkout and returnBook
To lend a book we write a checkout method; to take it back we write a returnBook method. Both take an index and change the borrowed field of the matching book.
Example: void checkout(int index) { books[index].borrowed = true; }. This method sets borrowed to true for the book at the given index. returnBook sets it to false.
This structure is the basis of lending. When a book is lent borrowed becomes true; when returned it becomes false. The index parameter tells which book is processed.
Taking a book back
The returnBook method does the reverse of checkout. With books[index].borrowed = false it marks the book as returned. This way the same book can be lent again.
Example flow: lib.addBook(Book('Les Miserables'));, lib.checkout(0);, print(lib.books[0].borrowed); gives true. Then lib.returnBook(0);, print(lib.books[0].borrowed); gives false.
These two methods form the lending cycle together. A book goes out, comes back, goes out again. This is how a library system works.
Practice Add checkout and returnBook
Add void checkout(int index) and void returnBook(int index) methods to the Library class. Inside checkout write books[index].borrowed = true; inside returnBook write books[index].borrowed = false. The main already calls checkout and returnBook.
Starter code
class Book {
String title;
bool borrowed = false;
Book(this.title);
}
class Library {
List<Book> books = [];
void addBook(Book b) {
books.add(b);
}
// add the checkout and returnBook methods
}
void main() {
var lib = Library();
lib.addBook(Book('Les Miserables'));
lib.checkout(0);
print(lib.books[0].borrowed);
lib.returnBook(0);
print(lib.books[0].borrowed);
}Sample solution
class Book {
String title;
bool borrowed = false;
Book(this.title);
}
class Library {
List<Book> books = [];
void addBook(Book b) {
books.add(b);
}
void checkout(int index) {
books[index].borrowed = true;
}
void returnBook(int index) {
books[index].borrowed = false;
}
}
void main() {
var lib = Library();
lib.addBook(Book('Les Miserables'));
lib.checkout(0);
print(lib.books[0].borrowed);
lib.returnBook(0);
print(lib.books[0].borrowed);
}Expected output
true false
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the checkout parts
| Term | Meaning |
|---|---|
int index |
Index parameter |
books[index] |
Book at index |
.borrowed = true |
Lend out |
.borrowed = false |
Take back |
2 What does checkout(0) do?
void checkout(int index) {
books[index].borrowed = true;
}- Lends all books out
- Removes the first book
- Sets borrowed of the first book to true Correct answer
- Prints the list
Explanation: checkout(0) sets borrowed of the book at index 0 to true.
3 The borrowed assignment
void checkout(int index) {
books[index].borrowed = ____;
}void checkout(int index) {
books[index].borrowed = true;
}Explanation: checkout sets borrowed to true.