类（面向对象）

类的声明和构造函数

class Person {
  String name;
  int age;

  Person(this.name, this.age);  // 这是构造函数，是简化写法，等价于下面的代码
  // Person(String name, int age){
  //   this.name = name;
  //   this.age = age;
  // }

  void sayHello() {
    print('hello $name, you are $age years old');
  }
}

继承

class Student extends Person {
  int id;

  Student(String name, int age, this.id) : super(name, age);

  @override
  void sayHello() {
    print('hello $name, you are $age years old, your id is $id');
  }
}

工厂构造函数

class Student extends Person {
  int id;

  factory Student.fromJson(Map<String, dynamic> json) {
    return Student(json['name'], json['age'], json['id']);
  }
}

枚举类

enum Gender {
  male,
  female,
}

// 枚举类的使用
Gender gender = Gender.male;
print(gender);