js 对象的封装，继承，多态的理解

//对象的继承，这里采用构造函数继承+类式继承
function Person(name,sex,age){
	this.name = name;
	this.sex = sex;
	this.age = age;
}

Person.prototype.getName = function(){
	return this.name;
}

function Student(school,name,sex,age){
	Person.call(this,name,sex,age);//构造函数继承，保证实例之间不会互相影响
	this.school = school;
}

Student.prototype = new Person();//类式继承，解决构造函数继承不能继承定义在外面的原型链的方法

var student1 = new Student("西都小学1","1","男1",21);
var student2 = new Student("西都小学2","2","男2",22);

console.log(student1.getName());//1
student1.name = "修改";
console.log(student1.name);//修改
console.log(student2.name);//2

//多态就是构造函数根据传入的变量不同，对同一方法，有不同的返回结果
//比如
function Math(){
	function zero(){
		return 10;
	}
	function one(num){
		return 10+num;
	}
	this.add = function(){
		switch(arguments.length){
			case 0:
				return zero();
				break;
			case 1:
				return one(arguments[0]);
				break;
		}
	}
}
var math1 = new	Math();
console.log(math1.add());//10
console.log(math1.add(10));//20

//封装就是有些私有的属性和方法，用户只能通过公有方法去访问这些私有属性
function Company(name){
	var personNum = 0;
	this.name = name;
	this.getNum = function(){
		return personNum;
	}
	this.addNum = function(){
		personNum++;
	}
}
var company1 = new Company("保时捷");
var company2 = new Company("宝马");
console.log(company1.getNum());//0
company1.addNum();
console.log(company1.getNum());//1
console.log(company2.getNum());//0
console.log(company1.personNum);//undefined