第四部分 方法4---------------

从构造器调用虚拟方法

    当我们实例化一个派生的SalariedEmployee对象时,运行的第一个构造器是基本的Employee构造器,它调用派生的SalariedEmployee.CaluculatePay 方法.但是，这个调用发生在派生的SalariedEmployee构造器之前.因此,附加的SalariedEmployee字段还没有被初始化:

using System;
using System.Collections.Generic;
using System.Text;

namespace csharpMethod
...{
    class Employee
    ...{
        public string name;
        public Employee(string name)
        ...{
            this.name = name;
            Console.Write("Employee.CalculatePay: ");
            CalculatePay();
        }
        public virtual void CalculatePay()
        ...{
            Console.WriteLine("Employee.CalculatePay called for {0}", name);

        }
    }
    class SalariedEmployee : Employee
    ...{
        public decimal salary;
        public SalariedEmployee(string name, decimal salary)
            : base(name)
        ...{
            this.salary = salary;
            Console.WriteLine("SalariedEmployee.CalculatePay: ");
            CalculatePay();
        }
        public override void CalculatePay()
        ...{
            Console.WriteLine("{0},SalariedEmployee,salary={1:C}", name, salary);

        }
    }
    class ContractEmployee : Employee
    ...{
        public double rate;
        public ContractEmployee(string name, double rate)
            : base(name)
        ...{
            this.rate = rate;
            Console.Write("ContractEmployee.CalculatePay: ");
            CalculatePay();

        }
        public override void CalculatePay()
        ...{
            Console.WriteLine("{0},SalariedEmployee,salary={1:C}", name, rate);
        }
    }
    
    class Test
    ...{
        protected Employee[] employees;
        static void Main(string[] args)
        ...{
            Employee[] employees = new Employee[2];
            employees[0] = new ContractEmployee("Adam Barr", 123.45);
            employees[1] = new SalariedEmployee("Max Benson", 67890m);
        }
    }
}