Explain the code

test.dart

void main() {
  var _patient = Patient();
  var _covidPatient = CovidPatient();
  var _testResult = TestResult();
  
  _patient.setPatientData("Tuhin", "Male", 24);
  print(_patient.patientData.values);

  _covidPatient.name = "John";
  print(_covidPatient.name);

  _testResult.testResult = "Positive";

  _covidPatient.isInfected = _testResult.testResult;

  print(_covidPatient.isInfected);
}

class Patient {
  String _name;
  String _gender;
  int _age;

  Map<String, dynamic> get patientData {
    return {"name": _name, "gender": _gender, "age": _age};
  }

  setPatientData(String name, String gender, int age) {
    this._name = name;
    this._gender = gender;
    this._age = age;
  }
  //Patient(this.name, this.gender, this.age);
  set name(String name) => this._name = name;

  String get name => _name;
}

class CovidPatient extends Patient {
  bool _isInfected;

  set isInfected(String result) =>
      result == "Positive" ? _isInfected = true : _isInfected = false;

  get isInfected => _isInfected;
}

class TestResult {
  String _testResult;

  set testResult(String result) => this._testResult = result;

  String get testResult => _testResult;
}