Object in Dart

Object In Dart

In object-oriented programming, an object is a self-contained unit of code and data. Objects are created from templates called classes. An object is made up of properties(variables) and methods(functions). An object is an instance of a class.

For example, a bicycle object might have attributes like color, size, and current speed. It might have methods like changeGear, pedalFaster, and brake.

Info

Note: To create an object, you must create a class first. It’s a good practice to declare the object name in lower case.

Instantiation

In object-oriented programming, instantiation is the process of creating an instance of a class. In other words, you can say that instantiation is the process of creating an object of a class. For example, if you have a class called Bicycle, then you can create an object of the class called bicycle.

Declaring Object In Dart

Once you have created a class, it’s time to declare the object. You can declare an object by the following syntax:

Syntax

ClassName objectName = ClassName();

Example 1: Declaring An Object In Dart

In this example below, there is class Bycycle with three properties: color, size, and currentSpeed. The class has two methods. One is changeGear, which changes the gear of the bicycle, and display method prints out the values of the three properties. We also have an object of the class Bycycle called bicycle.

    class Bicycle {
      String? color;
      int? size;
      int? currentSpeed;
    
      void changeGear(int newValue) {
        currentSpeed = newValue;
      }
    
      void display() {
        print("Color: $color");
        print("Size: $size");
        print("Current Speed: $currentSpeed");
      }
    }

    void main(){
        // Here bicycle is object of class Bicycle. 
        Bicycle bicycle = Bicycle();
        bicycle.color = "Red";
        bicycle.size = 26;
        bicycle.currentSpeed = 0;
        bicycle.changeGear(5);
        bicycle.display();
    }

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Info

Note: Once you create an object, you can access the properties and methods of the object using the dot(.) operator.

Example 2: Declaring Animal Class Object In Dart

In this example below there is class Animal with three properties: name, numberOfLegs, and lifeSpan. The class also has a method called display, which prints out the values of the three properties. We also have an object of the class Animal called animal.

class Animal {
      String? name;
      int? numberOfLegs;
      int? lifeSpan;
    
      void display() {
        print("Animal name: $name.");
        print("Number of Legs: $numberOfLegs.");
        print("Life Span: $lifeSpan.");
      }
    }

    void main(){
        // Here animal is object of class Animal. 
        Animal animal = Animal();
        animal.name = "Lion";
        animal.numberOfLegs = 4;
        animal.lifeSpan = 10;
        animal.display();
    }

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Example 3: Declaring Car Class Object In Dart

In this example below there is class Car with three properties: name, color, and numberOfSeats. The class also has a method called start, which prints out the message “Car Started”. We also have an object of the class Car called car.

    class Car {
      String? name;
      String? color;
      int? numberOfSeats;
    
      void start() {
        print("$name Car Started.");
      }
    }

    void main(){
        // Here car is object of class Car. 
        Car car = Car();
        car.name = "BMW";
        car.color = "Red";
        car.numberOfSeats = 4;
        car.start();

        // Here car2 is another object of class Car.
        Car car2 = Car();
        car2.name = "Audi";
        car2.color = "Black";
        car2.numberOfSeats = 4;
        car2.start();
    }

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Key Points

  • The main method is the program’s entry point, so it is always needed to see the result.
  • The new keyword can be used to create a new object, but it is unnecessary.

Challenge

Create a Class Camera with properties: name, color, megapixel. Create a method called display which prints out the values of the three properties. Create two objects of the class Camera and call the method display.

Video

Watch our video on parameterized constructor in Dart.