C#Protected和多态（虚方法）

Protected 在基类中定义后，能被派生类调用，但是不能被其他类调用。

virtual 在基类中定义后，在派生类中能被重写。

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

namespace 继承
{
    class Vertebrate
    {
        protected string spine;//受保护的字段
        private double weigth;
        private double temperature;
        public double Weigth
        {
            set
            {
                if (value < 0)
                {
                    weigth = 0;
                }
                else
                {
                    weigth = value;
                }
            }
            get { return weigth; }
        }
        public double Temperature
        {
            set
            {
                if (value < 0)
                {
                    temperature = 0;
                }
                else
                {
                    temperature = value;
                }
            }
            get { return temperature; }
        }
        public Vertebrate()
        {
            spine = "脊柱";
            weigth = 0;
            temperature = 0;
        }
        public virtual  void Breate() //虚方法
        {
            Console.WriteLine("呼吸");
        }
        public void Sleep()
        {
            Console.WriteLine("睡觉");
        }
    }
}

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

namespace 继承
{
    class Program
    {
        static void Main(string[] args)
        {
            Vertebrate vertebrate = new Vertebrate();
            vertebrate.spine1 = "脊柱"; //public的就能被直接调用
            Mammal mammal = new Mammal();
            Fish fish = new Fish();
            Animal animal = new Animal();
            Console.WriteLine("我是一只哺乳动物");
            mammal.Scukle();
            animal.Breate();
            mammal.Breate();
            fish.Breate();
            mammal.Sleep();
            mammal.Message();
        }
    }
    class Fish : Vertebrate
    {
        public override void Breate()//重写基类中的虚方法
        {
            Console.WriteLine("用鳃呼吸");
        }
    }
    class Animal : Vertebrate
    {

    }
    class Mammal : Vertebrate//派生类：基类
    {
        private string arms;
        private string legs;
        private int age;
        public int Age
        {
            set { age = value; }
            get { return age; }
        }
        public Mammal()
        {
            arms = "前肢";
            legs = "后肢";
            Age = 0;
            Weigth = 10;
            Temperature = 37;
        }
        public void Scukle()
        {
            Console.WriteLine("哺乳");
        }
        public override void Breate()
        {
            Console.WriteLine("用肺呼吸");
        }
        public void Message()
        {
            Console.WriteLine("体重：{0}", Weigth);
            Console.WriteLine("年龄：{0}", Age);
            Console.WriteLine("体温：{0}", Temperature);
            Console.WriteLine("我有{0}和{1}", arms, legs);
        }
    }
}