Parameterized Constructor in Dart

Parameterized Constructor

Parameterized constructor is used to initialize the instance variables of the class. Parameterized constructor is the constructor that takes parameters. It is used to pass the values to the constructor at the time of object creation.

Syntax

class ClassName {
  // Instance Variables
  int? number;
  String? name;
  // Parameterized Constructor
  ClassName(this.number, this.name);
}

Example 1: Parameterized Constructor In Dart

In this example below, there is a class Student with three properties: name, age, and rollNumber. 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 Student called student.

class Student {
  String? name;
  int? age;
  int? rollNumber;
  // Constructor
  Student(this.name, this.age, this.rollNumber);
}

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

Name: John
Age: 20
Roll Number: 1

Example 2: Parameterized Constructor With Named Parameters In Dart

In this example below, there is a class Student with three properties: name, age, and rollNumber. 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 Student called student.

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

  // Constructor
  Student({String? name, int? age, int? rollNumber}) {
    this.name = name;
    this.age = age;
    this.rollNumber = rollNumber;
  }
}

void main(){
    // Here student is object of class Student. 
    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: Parameterized Constructor With Default Values In Dart

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

class Student {
  String? name;
  int? age;

  // Constructor
  Student({String? name = "John", int? age = 0}) {
    this.name = name;
    this.age = age;
  }
}

void main(){
    // Here student is object of class Student. 
    Student student = Student();
    print("Name: ${student.name}");
    print("Age: ${student.age}");
}

Name: John
Age: 0

Video

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