关键字override有用吗？

[plottowan_1977]

感觉override关键字没啥用，有没有都一样重载，以MSDN上的一个例子

using System;
class TestOverride
{
    public class Employee
    {
        public string name;

        // Basepay is defined as protected, so that it may be 
        // accessed only by this class and derrived classes.
        protected decimal basepay;

        // Constructor to set the name and basepay values.
        public Employee(string name, decimal basepay)
        {
            this.name = name;
            this.basepay = basepay;
        }

        // Declared virtual so it can be overridden.
        public virtual decimal CalculatePay()
        {
            return basepay;
        }
    }

    // Derive a new class from Employee.
    public class SalesEmployee : Employee
    {
        // New field that will affect the base pay.
        private decimal salesbonus;

        // The constructor calls the base-class version, and
        // initializes the salesbonus field.
        public SalesEmployee(string name, decimal basepay, 
                  decimal salesbonus) : base(name, basepay)
        {
            this.salesbonus = salesbonus;
        }

        // Override the CalculatePay method 
        // to take bonus into account.
        public override decimal CalculatePay()
        {
            return basepay + salesbonus;
        }
    }

    static void Main()
    {
        // Create some new employees.
        SalesEmployee employee1 = new SalesEmployee("Alice", 
                      1000, 500);
        Employee employee2 = new Employee("Bob", 1200);

        Console.WriteLine("Employee " + employee1.name + 
                  " earned: " + employee1.CalculatePay());
        Console.WriteLine("Employee " + employee2.name + 
                  " earned: " + employee2.CalculatePay());
    }
}

运行结果是
Employee Alice earned: 1500
Employee Bob earned: 1200

如果，我把例子中CalculatePay函数前的override关键字都去掉
结果一样
说明在类SalesEmployee中已经重载了CalculatePay，那还要override做什么呢？

[flyfly2008]

应该有用吧！不过我不知道，过来等高手回答

[qinxiaoasxzas]

要扩展或修改继承的方法、属性、索引器或事件的抽象实现或虚实现，必须使用 override 修饰符。

[tkscascor]

Employee employee2 = new Employee("Bob", 1200);
Employee employee1 = new SalesEmployee("Alice", 1000, 500);

兄台.. 多态是这样用的

[tkscascor]

根据实例的对象,来调用不同的方法.

[MaokFly]

重写

[yymycabbage]

override表示对继承方法的重写，可以实现多态。
lz把main代码改成如下，加关键字的结果还是一样，如果不加override的话，结果就是

Employee Alice earned: 1000
Employee Bob earned: 1200

不加override表示跟父类的同名函数脱离继承关系，没有办法实现多态。
c#设计的一个原则就是要求明确表达代码意图，所以要求重写的方法前面必须加override。

        static void Main()
        {
            // Create some new employees.
            Employee employee1 = new SalesEmployee("Alice",
                          1000, 500);
            Employee employee2 = new Employee("Bob", 1200);

            Console.WriteLine("Employee " + employee1.name +
                      " earned: " + employee1.CalculatePay());
            Console.WriteLine("Employee " + employee2.name +
                      " earned: " + employee2.CalculatePay());
        }

[plottowan_1977]

有道理