接口实现和虚方法重写

继承接口和继承基类的实例如下

public class Animal
{
    public virtual void Eat()
    {
        Console.WriteLine("Animal is eating!");
    }
}
public class Lion{}
public class Bird:Animal
{
    public override void Eat()
    {
        Console.WriteLine("Bird is eating!");
    }
    public virtual void Build()
    {
        Console.WriteLine("Bird is building nest!");
    }
}
public class Person:Animal
{
    public override void Eat()
    {
        Console.WriteLine("Person is eating!");
    }
    public virtual void Build()
    {
        Console.WriteLine("Person is building house!");
    }
}
public class Chinese:Person
{
    public override void Eat()
    {
        Console.WriteLine("Chinese is eating!");
    }
    public override void Build()
    {
        Console.WriteLine("Chinese is building the Great Wall!");
    }
}

 基类Animal有一个Eat虚方法，子类Person重写Eat，子类Lion不做任何操作，Person调用的是重写后的Eat，Lion则调用基类的Eat；在Person和Bird中又分别定义了Build虚方法，在每一个类中分别去定义Build显然是不合理的（但是有人觉得没毛病，哈哈哈哈），此时可以将Build抽出来放到接口中，Person和Bird实现该接口，修改代码如下

public class Bird:Animal,IAction
{
    public override void Eat()
    {
        Console.WriteLine("Bird is eating!");
    }
    public void Build()
    {
        Console.WriteLine("Bird is building nest!");
    }
}
public class Person:Animal,IAction
{
    public override void Eat()
    {
        Console.WriteLine("Person is eating!");
    }
    public void Build()
    {
        Console.WriteLine("Person is building house!");
    }
}
public class Chinese:Person
{
    public override void Eat()
    {
        Console.WriteLine("Chinese is eating!");
    }
}
public interface IAction
{
    public void Build();
}

那么问题就来了，实现接口中的Build和重写基类中的Build的区别是什么呢？当然不是指代码量上的区别

对比Eat和Build，可以看到Person的基类Chinese仍然可以重写Eat方法，而不能显示实现接口IAction中的Build方法，此时子类Chinese中使用的Build是其基类Person中实现的Build，那么如何在子类Chinese中实现对Build方法的“重写”？此时就要使用new关键字了，之前一直没想到new隐藏方法的使用场景是什么。。。修改代码如下

public class Chinese:Person
{
    public override void Eat()
    {
        Console.WriteLine("Chinese is eating!");
    }
    public new void Build()
    {
        Console.WriteLine("Chinese is building the Great Wall!");
    }
}

此时子类Chinese中的new表示隐藏了其基类Person中的Build方法，也可以在Person类中将实现的接口方法声明为Virtual，这样Chinese类中也可以直接对Build方法进行重写，代码如下

public class Person:Animal,IAction
{
    public override void Eat()
    {
        Console.WriteLine("Person is eating!");
    }
    public virtual void Build()
    {
        Console.WriteLine("Person is building house!");
    }
}
public class Chinese:Person
{
    public override void Eat()
    {
        Console.WriteLine("Chinese is eating!");
    }
    public override void Build()
    {
        Console.WriteLine("Chinese is building the Great Wall!");
    }
}
public interface IAction
{
    public void Build();
}