What is Dart Constructor?

A Dart constructor is a special function that initialises the variables in the class. Dart uses the class name to name the constructor.

Besides, since a constructor is a function, we can pass parameters through it. 

However, the number of parameters may vary. Number of parameters changes with the number of the variables.

We will see that in a minute.

For example we consider a class Car.

Let’s see the code first, after that, we will discuss the code.

class Car {
  int accelerator;
  int _speed = 0;
  int get speed => _speed;
  int gear;

  Car(this.accelerator, this.gear);

  int brake(int applyPressureOnBrake) {
    _speed -= applyPressureOnBrake * 10;
    return _speed;
  }

  int accelerate(int pressureOnAccelerator) {
    _speed += 10 * pressureOnAccelerator;
    return _speed;
  }

  @override
  String toString() => 'Car: $_speed mph';
}

void main() {
  var bike = Car(0, 0);
  print(bike);
  bike._speed = bike.accelerate(2);
  print('When the pressure on Accelerator is 2, the speed is ${bike._speed}');
  bike._speed = bike.brake(2);
  print('When the pressure on Brake is 2, the speed is ${bike._speed}');
}

In the previous section we have seen how we can use the private variable by using the get method.

Let us run the code. And see the output first.

Car: 0 mph
When the pressure on Accelerator is 2, the speed is 20
When the pressure on Brake is 2, the speed is 0

Let us look at the member variables first. Between three, one is private. 

As a result, we have made it public by using the get method so that we can use them later.

int _speed = 0;
int get speed => _speed;

Not only that, according to the rule, we have declared a constructor and passed two variables as its parameters.

Car(this.accelerator, this.gear);

As an outcome, when we create an object, we need to pass two values.

Initially, when the car has no accelerator and no gear, it has no speed.

var bike = Car(0, 0);
print(bike);
// output: Car: 0 mph

However, when we call the methods, the output changes.

How the dart methods work, we’ll discuss in the next section.

So stay tuned. 

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