有一个abstract类，类名为Employee

要求有一个abstract类，类名为Employee。Employee的子类有YearWorker、MonthWorker和WeekWorker。YearWorker对象按年薪领取薪水，MonthWorker按月领取薪水，WeekWorker按周领取薪水。Employee类有一个abstract方法：Public abstract earnings（）；子类必须重写父类的earnings（）方法，给出各自领取报酬的具体方式。有一个Company类，该类用Employee数组作为成员，Employee数组的单元可以是YearWorker对象的上转型对象、MonthWorker对象的上转型对象或WeekWorker对象的上转型对象。程序能输出Company对象一年需要支付的薪水总额。

package homework;
/*
File name:Company.cpp
Author:杨柳
Date:2017/11/6
IDE:eclipse
*/
class Company {
	Employee[] em; //Employee作为成员
    Company(Employee[] em) { //构造函数
    	this.em=em;	
    } 
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Employee[] em=new Employee[3];
		em[0]=new YearWorker(1,12000.0); //上转型对象
		em[1]=new MonthWorker(11,8000.0);
		em[2]=new WeekWorker(40,1200.0);
		Company com=new Company(em);
		double sum;
		sum=em[0].earnings()+em[1].earnings()+em[2].earnings();
		System.out.println("总工资为:"+sum);

	}

}
abstract class Employee {
	abstract double earnings(); //抽象方法
}
class MonthWorker extends Employee {
	int month;
	double monthSalary;
	MonthWorker(int m,double s){
		month=m;
		monthSalary=s;
	}
    double earnings() {
		return month*monthSalary;
	}

}
class WeekWorker extends Employee {
	int week;
	double weekSalary;
	WeekWorker(int w,double s){
		week=w;
		weekSalary=s;
	}
    double earnings() {
		return week*weekSalary;
	}
}
class YearWorker extends Employee {
	int year;
	double yearSalary;
	YearWorker(int y,double s){ //工作年数，年工资
		year=y;
		yearSalary=s;
	}
    double earnings() {  //重写抽象方法
		return year*yearSalary;
	}

}