Constructors - Dart Programming

A generative constructor with this.x assigns positional arguments to final fields. Named constructors give a class extra ways to build itself, with an initializer list : x = ..., y = ... setting the fields before the body runs.

Program

Play the program to build a Point three different ways.

constructors.dart

class Point {
  final int x;
  final int y;
  Point(this.x, this.y);
  Point.origin() : x = 0, y = 0;
  Point.diagonal(int n) : x = n, y = n;
}

void main() {
  var a = Point(3, 4);
  var b = Point.origin();
  var c = Point.diagonal(5);
  print('${a.x},${a.y} ${b.x},${b.y} ${c.x},${c.y}');
}

generative `Point(this.x, this.y)` assigns straight to `final` fields from positional arguments.

named constructor `Point.origin()` and `Point.diagonal(n)` are extra named ways to build a `Point`.

initializer list `: x = 0, y = 0` runs before the body and is required when `final` fields need values.