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);
        }
    }
}