public/subjects/mobile-dev/person

Person

Instructions

Create a class named Person.

Its attributes:

• name: string
• surname: string
• cityOfOrigin: string
• age: int
• height: int

Constructor:

• name: required
• cityOfOrigin: required
• age: required
• height: required
• surname: optional

Object Oriented Programming

Dart supports object oriented programming, and it features heavily in Flutter. Classes have 2 main concepts.

• Attributes: store data about the instance of a class.
• Methods: are func functions, which can use class attributes for various manipulations.

Here is an example of a class in Dart. Point is the name of the class, while x and y are attributes:

class Point {
  // Attributes initialized to 0.
  double x = 0;
  double y = 0;
}

What if you want to initiate a Point with different x and y? We use constructors to solve this problem. A constructor is a function which specifies how to instantiate an instance of a class, from a set of given parameters.

class Point {
  // Attributes initialized to 0.
  double x = 0;
  double y = 0;

  // Constructor
  Point(double x, double y) {
    // Sets the attributes to the value of the constructor arguments.
    this.y = y;
    this.x = x;
  }
}

In Dart we can also use constructor declaration to save a few lines of code.

class Point {
  // The constructor initializes the attributes.
  // Attributes do not need to be initialized as soon as the are declared.
  double x;
  double y;

  Point(this.x, this.y);
}

Now let's instantiate two objects of class Point:

var p1 = Point(5, 4);
var p2 = Point(8, 3);

Suppose we want to know the distance between these 2 points? We can do that by declaring a method, and passing one of the objects as a parameter:

import 'dart:math';

class Point {
  double x;
  double y;

  Point(this.x, this.y);

  // Method
  double distanceTo(Point end) {
    return sqrt(pow((end.x - this.x), 2) + pow((end.y - this.y), 2));
  }
}

void main() {
  var p1 = Point(5, 4);
  var p2 = Point(8, 3);

  print(p1.distanceTo(p2));
}

Check out the class section of the dart language tutorial.