面向对象

概念

类-模板

对象-实例

// 类-模板
class People {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }
  eat() {
    console.log(`${this.name} 吃 饭饭 `);
  }
  speak() {
    console.log(`我叫 ${this.name}，今年 ${this.age} 岁`);
  }
}

// 对象-实例
const p1 = new People("黄金胡", 18);

p1.eat();
p1.speak();

三要素

继承，子类继承父类

class People {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }
  eat() {
    console.log(`${this.name} 吃 饭饭 `);
  }
  speak() {
    console.log(`我叫 ${this.name}，今年 ${this.age} 岁`);
  }
}

class Student extends People {
  weight(weight) {
    throw new Error("Method not implemented.");
  }
  getWeight() {
    throw new Error("Method not implemented.");
  }
  constructor(name, age, number) {
    super(name, age);
    this.number = number;
    this.girlfriend = undefined;
  }
  study() {
    alert(`${this.name} 学习`);
  }
}

const s1 = new Student("黄大仙", 66, "00252054");
s1.eat();
s1.speak();
s1.study();

封装，数据的权限和保密
- public 完全开放
- protected 对子类开放
- private 对自己开放
js 中没有上述 3 个关键字，ts 有
- 减少耦合，不该外露的不外露
- 利于数据、接口的权限管理
- ES6 目前不支持，一般认为_开头的属性是 private

class People {
  name: String;
  age: Number;
  protected weight: Number; //受保护的属性，只有自己或者子类可以访问
  constructor(name: String, age: Number) {
    this.name = name;
    this.age = age;
    this.weight = 120;
  }
  eat() {
    alert(`${this.name} eat something`);
  }
  speak() {
    alert(`My name is ${this.name}, age ${this.age}`);
  }
}

//子类继承父类
class Student extends People {
  number: String;
  private girlfriend;
  constructor(name: String, age: Number, number: String) {
    super(name, age);
    this.number = number;
    this.girlfriend = "xiaoli";
  }
  study() {
    alert(`${this.name} study`);
  }
  getWeight() {
    alert(`weight ${this.weight}`);
  }
}

let xiaoming = new Student("xiaoming", 10, "A1");
xiaoming.getWeight();
alert(xiaoming.girlfriend);
alert(xiaoming.weight);

多态，同一接口不同实现
- js 应用极少
- 需要结合 java 等语言的接口、重写、重载等功能
- 保持子类的开放性和灵活性
- 面向接口编程
- （js 引用极少，了解即可）

class People {
  constructor(name) {
    this.name = name;
  }
  saySomething() {}
}

class A extends People {
  constructor(name) {
    super(name);
  }
  saySomething() {
    alert("I am A");
  }
}

class B extends People {
  constructor(name) {
    super(name);
  }
  saySomething() {
    alert("I am B");
  }
}

let a = new A("a");
a.saySomething();
let b = new B("b");
b.saySomething();

为什么使用面向对象?

程序执行：顺序、判断、循环---结构化
面向对象---数据结构化
对于计算机，结构化才是最简单的
编程应该 简单&抽象