正文
[Dart] Understand Classes and Inheritance in Dart
提示：扫一扫查出行【扫一扫了解最新限行尾号】
复制提示
We will look at how we can create classes and explore some various features. Dart adopts a single-inheritance model, meaning that you can only extend a single class. We will therefore extend our class example by creating an Employee subclass of a parent Person class.
A normal class:
class Person {
String name;
int age;
Person(name, age) {
this.name = name;
this.age = age;
}
}
We can also use short hand syntax:
class Person {
String name;
int age;
Person(this.name, this.age);
}
We can have optional arguements, override operator, and getter, setter:
class Person {
// private name
String _name;
int age;
String occupaction;
// optional {this.occupation}
Person(this._name, this.age, {this.occupaction});
// optional [this.occupaction]
Person.fromJson(Map json, [this.occupaction]) {
_name = json['name'];
age = json['age'];
}
// override == operator, define a custom one
bool operator ==(dynamic b) => _name == b.name && age == b.age && occupaction == b.occupation;
String get name => _name;
void set name(String updateName) => _name = updateName;
speak() {
print("My name is &_name. I'm $age years old.");
}
}
Use:
void main() {
Person johnny = Person('Johnny', , occupaction: 'WD')
..speak(); // My name is &_name. I'm 42 years old.
Person jane = Person.fromJson({'name': 'Johnny', 'age': , 'occupation': 'WD'});
print(jane == johnny); // true
}
Here '..speak()' the same as:
Person johnny = Person('Johnny', , occupation: 'Pilot')
johnny.speak()
---
void main() {
Person johnny = Person('Johnny', 42, occupation: 'Pilot')
..speak()
..name = 'Big Johnny'
..speak();
print(johnny.name);
print(johnny.occupation);
Person jane = Person.fromJson({'name': 'Jane', 'age': 39}, 'Web Developer');
jane.speak();
print(jane.occupation);
print(johnny == jane);
Person jane2 = Person('Jane', 39, occupation: 'Web Developer');
print(jane == jane2);
var bob = Employee('Bob', 23, DateTime.now());
bob.speak();
}
class Employee extends Person {
Employee(String name, int age, this.joinDate): super(name, age);
final DateTime joinDate;
@override
speak() {
print('My name is $name. I joined on $joinDate');
}
}
class Person {
Person(this._name, this.age, {this.occupation});
Person.fromJson(Map json, [this.occupation]) {
_name = json['name'];
age = json['age'];
}
String _name;
int age;
String occupation;
String get name => _name;
void set name(String updatedName) => _name = updatedName;
// If overriding the == operator, you should also override the Object's `hashCode` getter
// Learn more at https://www.dartlang.org/guides/libraries/library-tour#implementing-map-keys
bool operator ==(dynamic b) => _name == b.name && age == b.age && occupation == b.occupation;
speak() {
print("My name is $_name. I'm $age years old.");
}
// void _hiddenMethod() {
// print('This method is hidden');
// }
}
