Understanding Types of Constructors Class in Dart

In Dart, constructors are special methods used to initialize objects of a class. There are different types of constructors you can use, each with its unique purpose. In this blog, we’ll explore these constructors with simple examples for beginners. 🌟

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1. Default Constructor

A default constructor is automatically created by Dart if you don't define any constructor in your class. It has no parameters and provides a basic way to create objects.

Example:

class Student {
  String name = "Unknown";
  int age = 0;
}

void main() {
  Student student = Student(); // Using the default constructor
  print("Name: ${student.name}, Age: ${student.age}");
}

Output:

Name: Unknown, Age: 0

Here, Dart automatically provides a default constructor because we didn’t define one.

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2. Parameterized Constructor

A parameterized constructor allows you to pass values to initialize the instance variables of a class.

Example:

class Student {
  String name;
  int age;

  // Parameterized constructor
  Student(String name, int age) {
    this.name = name;
    this.age = age;
  }

  void display() {
    print("Name: $name, Age: $age");
  }
}

void main() {
  Student student = Student("Alice", 20); // Passing values to the constructor
  student.display();
}

Output:

Name: Alice, Age: 20

Here, we’re passing name and age as parameters to initialize the Student object.

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3. Named Constructor

Named constructors allow you to create multiple constructors in the same class by giving each a unique name. This is useful when you want to initialize objects differently based on the situation.

Example:

class Student {
  String name;
  int age;

  // Named constructor for regular students
  Student.regular(String name, int age) {
    this.name = name;
    this.age = age;
  }

  void display() {
    print("Name: $name, Age: $age");
  }
}

void main() {
  Student regularStudent = Student.regular("Bob", 22);
  regularStudent.display(); // Output: Name: Bob, Age: 22
}

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4. Constructor with this Keyword

You can simplify the parameterized constructor by using the this keyword to assign parameter values to instance variables.

Example:

class Student {
  String name;
  int age;

  // Constructor using 'this'
  Student(this.name, this.age);

  void display() {
    print("Name: $name, Age: $age");
  }
}

void main() {
  Student student = Student("Charlie", 18); 
  student.display();
}

Output:

Name: Charlie, Age: 18

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5. Redirecting Constructor

A redirecting constructor calls another constructor in the same class, avoiding code duplication.

Example:

class Student {
  String name;
  int age;

  // Main constructor
  Student(this.name, this.age);

  // Redirecting constructor
  Student.guest() : this("Guest", 0);
}

void main() {
  Student guestStudent = Student.guest();
  print("Name: ${guestStudent.name}, Age: ${guestStudent.age}");
}

Output:

Name: Guest, Age: 0

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Summary of Constructor Types

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Practice Challenge

Create a Book class with:

1. A parameterized constructor to initialize title and author.

2. A named constructor for an unknown book with the title "Unknown" and author "Anonymous."

3. A method to display book details.

Test both constructors in the main function! 💪

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With these constructor types in your toolkit, you’re now equipped to handle various object initialization scenarios in Dart. Keep practicing and experimenting! 😊