Constant Constructor in Dart

Constant Constructor In Dart

Constant constructor is a constructor that creates a constant object. A constant object is an object whose value cannot be changed. A constant constructor is declared using the keyword const.

Rule For Declaring Constant Constructor In Dart

• All properties of the class must be final.
• It does not have any body.
• Only class containing const constructor is initialized using the const keyword.

Example 1: Constant Constructor In Dart

In this example below, there is a class Point with two final properties: x and y. The class also has a constant constructor that initializes the two properties. The class also has a method called display, which prints out the values of the two properties.

class Point {
  final int x;
  final int y;

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

void main() {
  // p1 and p2 has the same hash code.
  Point p1 = const Point(1, 2);
  print("The p1 hash code is: ${p1.hashCode}");

  Point p2 = const Point(1, 2);
  print("The p2 hash code is: ${p2.hashCode}");
  // without using const
  // this has different hash code.
  Point p3 = Point(2, 2);
  print("The p3 hash code is: ${p3.hashCode}");

  Point p4 = Point(2, 2);
  print("The p4 hash code is: ${p4.hashCode}");
}

The p1 hash code is: 918939239
The p2 hash code is: 918939239
The p3 hash code is: 745146896
The p4 hash code is: 225789186

Example 2: Constant Constructor In Dart

In this example below, there is a class Student with three properties: name, age, and rollNumber. The class has one constant constructor. The constructor is used to initialize the values of the three properties. We also have an object of the class Student called student.

class Student {
  final String? name;
  final int? age;
  final int? rollNumber;

  // Constant Constructor
  const Student({this.name, this.age, this.rollNumber});
}

void main() {
  // Here student is object of Student.
  const Student student = Student(name: "John", age: 20, rollNumber: 1);
  print("Name: ${student.name}");
  print("Age: ${student.age}");
  print("Roll Number: ${student.rollNumber}");
}

Name: John
Age: 20
Roll Number: 1

Example 3: Constant Constructor With Named Parameters In Dart

In this example below, there is a class Car with three properties: name, model, and price. The class has one constructor. The constructor is used to initialize the values of the three properties. We also have an object of the class Car called car.

class Car {
  final String? name;
  final String? model;
  final int? price;

  // Constant Constructor
  const Car({this.name, this.model, this.price});
}

void main() {
  // Here car is object of class Car.
  const Car car = Car(name: "BMW", model: "X5", price: 50000);
  print("Name: ${car.name}");
  print("Model: ${car.model}");
  print("Price: ${car.price}");
}

Name: BMW
Model: X5
Price: 50000

Benefits Of Constant Constructor In Dart

• Improves the performance of the program.

Challenge

Create a class Customer with three properties: name, age, and phone. The class should have one constant constructor. The constructor should initialize the values of the three properties. Create an object of the class Customer and print the values of the three properties.

Video

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