Summary - Class basics

Combine class, constructor and methods to write a User class.

Summary - Class basics

This group covered class basics. class declares a class; the constructor prepares the instance; instance variables hold data; methods define behavior; this disambiguates field and parameter.

The short constructor User(this.name) equals the long User(String name) { this.name = name; }. The class name starts with a capital; an instance is created with User().

In the final task you will blend everything into a User class: both name and age fields, a constructor, and a describe method. This will be a small but real class.

Exercise User class with constructor

Define a User class with a String name field and a User(this.name) constructor. Inside main create a User('Ayşe') instance and print it with print(u.name).

Show example solution

class User {
  String name;
  User(this.name);
}

void main() {
  var u = User('Ayşe');
  print(u.name);
}

Exercise Full User class

Define a User class with String name and int age fields, a User(this.name, this.age) constructor, and a void describe() method. The method body should do print('$name, $age'). Inside main create a User('Ayşe', 28) instance and call u.describe().

Show example solution

class User {
  String name;
  int age;
  User(this.name, this.age);
  void describe() {
    print('$name, $age');
  }
}

void main() {
  var u = User('Ayşe', 28);
  u.describe();
}

Test yourself

Match the concepts

class

Class declaration
constructor

Instance preparation
instance variable

Data
this

This instance
When is the constructor called?
- When a method is called
- When the class is declared
- When an instance is created
- Never
Show answer

When an instance is created — the constructor is called when an instance is created.

Method call

void main() {
  var u = User('Ayşe');
  u.____();
}

Show answer

void main() {
  var u = User('Ayşe');
  u.describe();
}

Next lesson: Task model

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