Constructor

  • You can create an object using a constructor.
  • Constructor names can be either ClassName or ClassName.identifier.
  • Some classes provide constant constructors.
  • The most common form of constructor, the generative constructor, creates a new instance of a class.
  • Constructors aren’t inherited.

Invoking a non-default superclass constructor

class Person { 
   String firstName; 

   Person.fromJson(Map data) { 
   print('in Person'); 
   } 
} 

class Employee extends Person { 
   // Person does not have a default constructor; you must call super.fromJson(data). 
   Employee.fromJson(Map data) : super.fromJson(data) { 
   print('in Employee'); 
   } 
} 

main() { 
   var emp = new Employee.fromJson({}); 

   // Prints: 
   // in Person 
   // in Employee 
   if (emp is Person) { 
      // Type check 
      emp.firstName = 'Bob'; 
   } 
   (emp as Person).firstName = 'Bob'; 
}

Redirecting constructors

Sometimes a constructor’s only purpose is to redirect to another constructor in the same class.

A redirecting constructor’s body is empty, with the constructor call appearing after a colon (:).

Constructor — Structure map

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Constructor — Related pages: