面向对象

Posted 2022-01-06 沿着路走到底

面向对象三要素：继承、封装、多态

- 继承，子类继承父类

- 封装，数据的权限和保密

- 多态，同一接口不同实现

概念 -- 类

// 类，即模板
class People 
    constructor(name, age) 
        this.name = name
        this.age = age
    
    eat() 
        alert(`$this.name eat something`)
    
    speak() 
        alert(`My name is $this.name, age $this.age`)
    


// 创建实例
let zhang = new People('zhang', 20)
zhang.eat()
zhang.speak()

// 创建实例
let wang = new People('wang', 21)
wang.eat()
wang.speak()

三要素 -- 继承

- `People`是父类，公共的，不仅仅服务于`Student`

- 继承可将公共方法抽离出来，提高复用，极少冗余

// 父类
class People 
    constructor(name, age) 
        this.name = name
        this.age = age
    
    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 
    constructor(name, age, number) 
        super(name, age)
        this.number = number
    
    study() 
        alert(`$this.name study`)
    


let xiaoming = new Student('xiaoming', 10, 'A1')
xiaoming.study()
console.log(xiaoming.number)
let xiaohong = new Student('xiaohong', 11, 'A2')
xiaohong.study()

三要素 -- 封装

- 减少耦合，不该外露的不外露

- 利于数据、接口的权限管理

三要素 -- 多态

多态即执行同样的方法，不同对象会有不同表现。

保持子类的开放性和灵活性。

面向接口编程。

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()

面向对象的意义：数据结构化

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