Model design
- Dart course
- Intermediate
- Lesson 53/116
- 6 min
Design the skeleton of Book and Member classes.
Project: Library app
In this project you will build a library app. Each lesson adds a piece and the final lesson yields a working console app. The first step is the Book class that represents a single book.
A Book has two fields: String title (the book name) and bool borrowed (is it lent out?). When a Book is created borrowed defaults to false. The constructor Book(this.title) sets the title.
In the next lessons we will add a Library class, checkout and search methods. Starting with a solid model matters.
The Book class skeleton
The Book class looks like this: class Book { String title; bool borrowed = false; Book(this.title); }. The title is set by the constructor; borrowed keeps its default false.
Here bool borrowed = false gives the field an initial value. Book(this.title) is the short constructor; it assigns the title parameter straight to the field.
To use the Book write var b = Book('Les Miserables');. Read the name with b.title and the status with b.borrowed. The next lessons gather these Books in a list.
Practice Define the Book class
Define a Book class with String title, bool borrowed = false fields and a Book(this.title) constructor. Inside main create a Book('Les Miserables') instance; print title and borrowed on separate lines.
Starter code
void main() {
// define the Book class (outside main)
// create an instance and print title and borrowed
}Sample solution
class Book {
String title;
bool borrowed = false;
Book(this.title);
}
void main() {
var b = Book('Les Miserables');
print(b.title);
print(b.borrowed);
}Expected output
Les Miserables false
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the Book parts
| Term | Meaning |
|---|---|
String title |
Book name |
bool borrowed |
Lent status |
Book(this.title) |
Constructor |
false |
Initial value |
2 What is borrowed on a new Book?
- false Correct answer
- true
- null
- Throws
Explanation: on a new Book borrowed defaults to false.
3 Book constructor
class Book {
String title;
bool borrowed = false;
____(this.title);
}class Book {
String title;
bool borrowed = false;
Book(this.title);
}Explanation: the constructor shares the class name.