Object-oriented programming (OOP) is a programming paradigm that uses the idea of "objects" to represent data and methods. Dart, the programming language used to develop Flutter apps, is an object-oriented language. In this context, let's explore a fundamental aspect of OOP in Dart: the constructors.
Constructors in Dart are special functions that are used to create and initialize an object of a class. They have the same name as the class and can have parameters to initialize object attributes. Constructors are called when you create an instance of a class using the 'new' keyword.
To illustrate, let's consider a 'Car' class. This class can have attributes like 'brand', 'model' and 'year'. To initialize these attributes when we create a 'Car' object, we can use a constructor. See example below:
class Car {
String tag;
model string;
int year;
Car(String make, String model, int year) {
this.mark = mark;
this.model = model;
this.year = year;
}
}
Here, 'Car' is the constructor. It accepts three parameters and uses them to initialize the object's attributes. To create a 'Car' object, we would do the following:
Car myCar = new Car('Toyota', 'Corolla', 2020);
In this case, 'myCar' is an object of class 'Car'. Its 'brand' is 'Toyota', its 'model' is 'Corolla' and its 'year' is 2020.
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Dart also offers named constructors. These are constructors that have names in addition to the class name. They are useful when a class needs more than one constructor. For example, the class 'Car' can have a constructor named 'Car.Used' to create used cars:
class Car {
String tag;
model string;
int year;
Car(String make, String model, int year) {
this.mark = mark;
this.model = model;
this.year = year;
}
used.car(this.make, this.model) {
year = DateTime.now().year - 1;
}
}
Here, 'Used.car' is a named constructor. It accepts two parameters for 'make' and 'model', and sets 'year' to the year before the current year. To create a used car, we would do the following:
Car myCarUsed = new Car.used('Toyota', 'Corolla');
In Dart, we also have constant constructors. They are used to create immutable objects, that is, objects whose values cannot be changed after they are created. To create a constant constructor, we use the 'const' keyword.
Finally, Dart also offers the sugar syntax for constructors: variable initialization constructors. They allow you to initialize variables directly in constructor parameters, making the code more concise:
class Car {
String tag;
model string;
int year;
Car(this.brand, this.model, this.year);
}
Constructors are an essential part of object-oriented programming in Dart. They allow you to control how objects are created and initialized, providing greater flexibility and security in your code.
