实验：多态与继承

abstract class Employee{
   public abstract double earnings();
}
class YearWorker extends Employee{
  public double earnings() {//重写earnings()方法 50000元
   return 50000;
  }
}
class MonthWorker extends Employee{
 public double earnings(){//重写earnings()方法。2400元
 return 2400;
 }
}
class WeekWorker extends Employee{
 public double earnings(){//重写earnings()方法。400元
 return 400;
 }
}
class Company{
   Employee[] employee;//对象数组
   double salaries=0;
   Company(Employee[] employee){
      this.employee=employee;
   }
   public double salariesPay(){
      salaries=0;
      for(int i=0;i<employee.length;i++){
      salaries=salaries+employee[i].earnings(); //计算salaries。
      }
      return salaries;
   }   
}
public class HardWork{
   public static void main(String args[]){
      Employee[] employee=new Employee[20];//数组初始化
      for(int i=0;i<employee.length;i++){
           if(i%3==0)
             employee[i]=new WeekWorker();
           else if(i%3==1)
             employee[i]=new MonthWorker();
           else if(i%3==2)
             employee[i]=new YearWorker();
       }
     Company  company=new Company(employee);//调用Company的构造方法
     System.out.println("公司年工资总额:"+company.salariesPay());
   }
}

内存执行情况：

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