Flutter, Dart: When you specify a field name as a character string and want to get (access the field) that field

Question

class AAA{
  static int a=1;
  static int b=2;

  int c=3;
  int d=4;
}

void main(){

  print(AAA.a);  //1
  print(AAA.b);  //2

  String strA=\'a\';
  String strB=\'b\