Dart - 14 - Constructors and Named Constructors

Constructors and Named Constructors in Dart Programming

Constructors are essential elements of any object-oriented programming language, including Dart. They define how objects are created and initialized. Dart offers several ways to work with constructors, including standard constructors and named constructors, to provide flexibility and customization during object creation. In this discussion, we’ll explore the significance of constructors and named constructors in Dart, understand how they work, and see practical examples of their use.

Understanding Constructors

Constructors in Dart are special methods responsible for creating and initializing objects of a class. They determine how an object should be set up when it’s first instantiated. Constructors are essential for allocating memory and initializing attributes and other properties.

Default Constructor

Dart provides a default constructor if no constructor is explicitly defined. This default constructor takes no parameters and is responsible for initializing the object.

Here’s an example of a class with a default constructor:


class Person {
    String name;

    // Default constructor
    Person() {
        name = 'John Doe';
    }
}

In this example, the default constructor initializes the name attribute with the value ‘John Doe’ when a Person object is created.

Parameterized Constructors

Dart allows you to define constructors that accept parameters, also known as parameterized constructors. These constructors enable you to initialize object properties with values provided during object creation.

Here’s an example of a parameterized constructor:


class Book {
    String title;
    String author;

    // Parameterized constructor
    Book(this.title, this.author);
}

In this example, the Book class defines a parameterized constructor that accepts the title and author as arguments and assigns them to the corresponding object properties.

Named Constructors

Named constructors in Dart allow you to define multiple constructors within a class. Each constructor has a unique name and can be used for specific initialization scenarios or to provide alternative ways to create objects.

Here’s an example of a class with a named constructor:


class Rectangle {
    double width;
    double height;

    // Parameterized constructor
    Rectangle(this.width, this.height);

    // Named constructor
    Rectangle.square(double side) : width = side, height = side;
}

In this example, the Rectangle class has both a parameterized constructor for general rectangle creation and a named constructor Rectangle.square for creating square objects.

Using Constructors

To create objects in Dart, you can call constructors using the new keyword. Depending on the constructor type, you provide the necessary parameters for initialization.

Here’s an example of using constructors to create objects:


void main() {
    // Using the default constructor
    var person = Person();

    // Using the parameterized constructor
    var book = Book('Dart Programming', 'John Smith');

    // Using the named constructor
    var square = Rectangle.square(5.0);
}

Conclusion

Constructors are a vital part of Dart programming, responsible for creating and initializing objects. Whether using the default constructor, parameterized constructors, or named constructors, Dart offers flexibility and customization during object creation. Understanding and utilizing constructors is crucial for effective object-oriented programming in Dart.

Dart – 14 – Constructors and Named Constructors