javascript面向对象编程的学习---对象继承

继承,通俗地说,之前你写过一些类,这些类中有一些是而你现在要写的类的功能的子集或者基本相同,那么你不用完全重新写一个新的类,你可以把之前写的类拿过来使用.这样的一种代码重用过程就叫做继承.
    深入学习javascript继承之前,先了解下面的几个概念:
        父类:被继承的类
        子类:由继承得来的类
        超类:也就是父类
        抽象类:一般不用来实例化的类,它的用途是用来给其他类继承.
        基类:提供给其他类可以继承的类
        派生类:由基类继承而来的类

    javascript对象继承通常有下面的5种方式:
        1.对象冒充
        2.call()方式
        3.apply()方式
        4.原型链
        5.混合方式
  
    A.对象冒充
        所谓对象冒充,就是新的类冒充旧的类(旧的类必须采用构造函数方式),从而达到继承目的.
        eg.1
            function people(name,sex,age){    //使用构造函数方式
                this.name=name;
                this.sex=sex;
                this.age=age;
                this.say=function(){
                    alert("My name is "+this.name);
                };
                this.doing=function(){
                    alert("I am speaking");
                };
            }
            var Marry=new people("Marry","Woman","23");
            Marry.say();
            Marry.doing();
          
            function white_people(name,sex,age){
                this.inherit=people;
                this.inherit(name,sex,age);
                delete this.inherit;
              
                this.area=function(){
                    alert("I am in Europe");
                }
            }
            var Tom=new white_people("Tom","man","21");
            Tom.say();
            Tom.area();
            alert(Tom.age);
        上面的例子中,people是用来做white_people的基类,记住这个格式是用来对象冒充达到继承目的的
                this.inherit=people;            //冒充
                this.inherit(name,sex,age);        //继承
                delete this.inherit;            //删除继承
        所有新属性和新方法都必须再删除了继承后定义,这样是为了避免覆盖父类的相关属性和方法.
        另外,对象冒充支持多继承.
        eg.2
            function worker(pay,work){
                this.pay=pay;
                this.work=work;
            }
            function city_worker(name,sex,age,pay,work){
                this.inherit=people;
                this.inherit(name,sex,age);
                delete this.inherit;
              
                this.inherit=worker;
                this.inherit(pay,work);
                delete this.inherit;
            }
          
            var Jerry=new city_worker("Jerry","man","21","$1000","coder");
            Jerry.say();
            alert(Jerry.work);
        对象冒充有一个不足的地方:多继承机制实现时,如果基类存在相同的属性或者方法,将从后面的类继承.
      
    B.call()方式
        只是封装的对象冒充的一个函数.这样,我们不再需要写"经典"的三句话,而是用下面这句话代替:
            基类.call(对象,参数列表)
        eg.1
            function farmer(name,sex,age,pay,work){
                people.call(this,name,sex,age);
                worker.call(this,pay,work);
            }
          
            var Nicholas=new farmer("Nicholas","man","27","$3000","irrigator");
            Nicholas.say();
            alert(Nicholas.pay);
        同样,call()存在同名属性和方法的小问题.
      
    C.apply()方式
        和call()一样.apply()也是对象冒充的一个封装函数.其格式为:
            基类.apply(对象,参数数组);
        eg.1
            function white_collar(name,sex,age,pay,work){
                people.apply(this,new Array(name,sex,age));
                worker.apply(this,[pay,work]);
            }
          
            var Jiessie=new white_collar("Jiessie","woman","26","$2500","editor");
            Jiessie.say();
            alert(Jiessie.work);
        同样,apply()存在同名属性和方法的小问题.
      
    D.原型链
        上面三种方式都是采用构造函数方式的继承,对应地,也具有原型函数方式的继承:原型链.
        eg.1
            function blue_collar(){
            }
            blue_collar.prototype.name="Jean";
            blue_collar.prototype.age="33";
            blue_collar.prototype.say=function(){
                alert("my name is "+ this.name);
            };
          
            function city_blue_collar(){
            }
            city_blue_collar.prototype=new blue_collar();
          
            var jj=new city_blue_collar;
            jj.say();
        原型链也具有了原型链的缺点:不能传递参数.另外,原型链不支持多继承,因为
      
    E.混合方式
        使用构造函数方式来写类的属性,对属性的继承采用call()或者apply()
        使用原型方式来写的方法,对方法的继承采用原型链
        eg.1
            function beauty(name,age){
                this.name=name;
                this.age=age;
            }
            beauty.prototype.say=function(){
                alert("小女叫"+this.name);
            };
          
            function china_beauty(name,age,area){
                beauty.call(this,name,age);
                this.area=area;
            }
            china_beauty.prototype=new beauty();
            china_beauty.prototype.from=function(){
                alert("我来自"+this.area);
            };
          
            var diaochan=new china_beauty("貂禅","16","临洮");
            diaochan.say();
            diaochan.from();
            alert(diaochan.age);