# 
##  
In [Dart](https://www.educative.io/answers/what-is-dart), the `@required` annotation indicates that a named parameter must have a value assigned to it for the class where it is defined to work correctly.

It specifies that a named parameter is not optional.

> **Note:** Since the release of Dart 2.12(Null safety) and subsequent versions, the `@required` annotation is now replaced by the `required` keyword.

## Code

The following example shows how to use Dart's `@required` annotation.




class AddNum {
  final int x; 
  final int y; 

  AddNum({
    required this.x, // required parameter
    this.y = 1, // assigned default value
  });

  void displayMessage(){
    var sum = x + y; 
    print("Sum of $x and $y: $sum");
  }
}
void main() {
  
  var addNum = AddNum(x:10);
  addNum.displayMessage();

  print('Reassigning values =====');
  var addNumbers = AddNum(x:8, y: -5);
  addNumbers.displayMessage();
}

Dart required

## Explanation

- **Lines 1–14:** We defined a class called `AddNum`, which has two parameters, `x` and `y`, and a method called `displayMessage()`.
 In the `AddNum` class:

   - **Line 2:** We define the `x` parameter of type `int`. 
   - **Line 3:** We define the `y` parameter of type `int`. 
   - **Lines 5–8:** We define the class constructor. Next, we make the `x` parameter `required` and assign a default value to the `y` parameter.
   - **Lines 10–13:** We define the `displayMessage()` method that sum up the values of `x` and `y`, and display the result. 

- **Line 15:** We define the `main()` function.

- **Line 17:** We create an instance of the class `AddNum` and assign value to the `required` parameter `x`.

- **Line 18:** We called the `displayMessage()` method using the class's object `addNum`.

- **Line 20:** We use the `print()` function to display a message.

- **Line 21:** We create another class's object called `addNumbers` and reassign values to the parameters.

- **Line 22:** We called the `displayMessage()` method using the class's object `addNumbers`.


flutter.tar.gz

What is the @required annotation in Dart?

The @required annotation in Dart mandates that a named parameter must be provided value for correct class functionality. Replaced by required keyword in Dart 2.12+.