Is there a difference in how member variables are initialized in Dart?

Question

In Dart, is there a difference in assigning values right away vs in constructor like in Java?

class Example {
    int x = 3;
}

vs

class Example {
    int x;
    Example() {
        x = 3;
    }
}

I ask because when I was using Flutter and tried to assign a Function that uses setState to a variable, it was not possible with the former method but possible with the latter.

Answer 1

Using initializing formals when possible makes your code more terse.

class Point {
  double x, y;
  Point(this.x, this.y);
}

This this. syntax before a constructor parameter is called an “initializing formal”. You can’t always take advantage of it. Sometimes you want to have a named parameter whose name doesn’t match the name of the field you are initializing. But when you can use initializing formals, you should.

class Point {
  final num x;
  final num y;
  final num distanceFromOrigin;

  // Special syntax
  Point(this.x, this.y) :
    distanceFromOrigin = sqrt(pow(x, 2) + pow(y, 2));
}