Initialize a final variable in a constructor in Dart. Two ways but only one of them work? [duplicate] - flutter

Question

This question already has an answer here:
Is there a difference in how member variables are initialized in Dart?
(1 answer)
Closed 1 year ago.
I'm trying to understand the following example where I try to initialize a final variable in a constructor.
1st example - works
void main() {
Test example = new Test(1,2);
print(example.a); //print gives 1
}
class Test
{
final int a;
int b;
Test(this.a, this.b);
}
2nd example doesn't work
void main() {
Test example = new Test(1,2);
print(example.a); //compiler throws an error
}
class Test
{
final int a;
int b;
Test(int a, int b){
this.a = a;
this.b = b;
}
}
and when i remove final then it works again
void main() {
Test example = new Test(1,2);
print(example.a); //print gives 1
}
class Test
{
int a;
int b;
Test(int a, int b){
this.a = a;
this.b = b;
}
}
what is the difference between the constructor in the 1st and the 2nd constructor why final initialization works with the first and doesn't with the 2nd.
Can anyone explain that to me please?
THanks

Answer 1

You cannot instantiate final fields in the constructor body.
Instance variables can be final, in which case they must be set exactly once. Initialize final, non-late instance variables at declaration, using a constructor parameter, or using a constructor’s initializer list:
Declare a constructor by creating a function with the same name as
its class (plus, optionally, an additional identifier as described in
Named constructors). The most common form of constructor, the
generative constructor, creates a new instance of a class
syntax in the constructor (described in https://www.dartlang.org/guides/language/language-tour#constructors):