Model design

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.

Exercise 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.

Show example solution

class Book {
  String title;
  bool borrowed = false;
  Book(this.title);
}

void main() {
  var b = Book('Les Miserables');
  print(b.title);
  print(b.borrowed);
}

Test yourself

Match the Book parts

String title

Book name
bool borrowed

Lent status
Book(this.title)

Constructor
false

Initial value
What is borrowed on a new Book?
- false
- true
- null
- Throws
Show answer

false — on a new Book borrowed defaults to false.

Book constructor

class Book {
  String title;
  bool borrowed = false;
  ____(this.title);
}

Show answer

class Book {
  String title;
  bool borrowed = false;
  Book(this.title);
}

Next lesson: Library class

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