4- 类

1 -类方法

class Person{
    name:string
    age:number
    constructor(name:string,age:number){
        this.name = name;
        this.age = age;
    }
    getName():void{
        console.log(this.name);
    }
}
var p:Person = new Person("cheng",20);
p.getName();

class Person{
    /* 实例的name */
    name:string
    age:number
    getName():void{
        console.log(this.name);
    }
}
var p:Person = new Person();
p.getName();  // undefined
//当没有构造函数的时候,代码底层有自动补全构造函数

2- static

//static修饰的变量是类所共有的,只能通过类名去调用。
class Person{
    /* 实例的name */
    static skill:string = "js";
    name:string
    age:number
    getName():void{
        console.log(Person.skill)
        console.log(this.name);
    }
}
var p:Person = new Person();
p.getName();  // js  undefined

3.类的继承

//1.定义了一个Person类，包含name,age两个属性
Class Person{
    name:string;
  age:number;
  constructor(name:string,age:number){
          this.name=name;
        this.age=age;
  }
  sayName(){
      console.log(this.name)
  }
}
//2.extendsz子类会继承父类的属性和方法
class Students extends Person{
    skill:string;
  //super指父类，只能放在子类构造方法中的第一行
  constructor(name:string,age:number,skill:string){
      super(name,age);
    this.skill =skill;
  }
  saySkill():void{
      console.log(this.skill);
  }
}
var s:Student =new Student("lisi",18,"vue");
console.log(s);
s.sayName();

4- 多态

//根据传入的对象，动态决定调用谁的方法
interface Animal{
    eat():void;
}
class Cat implements Animal{
        eat():void{
            console.log("鱼")
    }
}
class Dog implements Animal{
        eat():void{
    console.log("骨头")
    }
}
class Farmer{
    feed(obj:Animal){
      obj.eat();
  }
}
var f:Farmer = new Farmer();
f.feed(new Cat());
f.feed(new Dog())