Constructor in Dart

In Dart, a constructor is a special method that is used to create and initialize an object of a class. When you create an instance of a class, the constructor sets up the initial state of that object.

Types of Constructors in Dart

1. Default Constructor:
   • If you don’t define a constructor in a class, Dart provides a default constructor. It is a no-argument constructor that initializes all fields to their default values.

   class Animal {
     // Dart provides a default constructor here
   }
   
   void main() {
     var cat = Animal();
   }
   

2. Parameterized Constructor:
   • You can define a constructor with parameters to initialize object properties with specific values.

   class Animal {
     String name;
     int age;
   
     // Parameterized constructor
     Animal(this.name, this.age);
   }
   
   void main() {
     var dog = Animal('Buddy', 3);
   }
   

3. Named Constructors:
   • You can create multiple constructors in a class using named constructors. This is useful when you need different ways to initialize an object.

   class Animal {
     String name;
     int age;
   
     // Named constructor
     Animal.withName(this.name);
     Animal.withAge(this.age);
   }
   
   void main() {
     var cat = Animal.withName('Whiskers');
     var parrot = Animal.withAge(2);
   }
   

4. Factory Constructors:
   • A factory constructor is a special type of constructor that can return an instance of a class or an existing instance, based on some logic. It is used when the creation process is complex or involves conditions.

   class Animal {
     String name;
   
     Animal._internal(this.name);
   
     // Factory constructor
     factory Animal(String name) {
       if (name == 'Dog') {
         return Animal._internal('Buddy');
       }
       return Animal._internal(name);
     }
   }
   
   void main() {
     var dog = Animal('Dog'); // Outputs: Buddy
   }
   

Constructors are essential for initializing the objects with desired properties and ensuring they are set up correctly.