C#基础继承和多态详解

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

public class Person
{

    private string _id;
    public string id
    {
        get { return _id; }
        set { _id = value; }
    }

    /// <summary>
    /// 构造函数
    /// </summary>
    /// <param name="id"></param>
    public Person(string id)
    {
        _id = id;
    }

    /// <summary>
    /// 无参构造函数
    /// </summary>
    /// <param name="id"></param>
    /// <param name="Class"></param>
    public Person()
    {
    }

    public string GetID()
    {
        return id;
    }

}

//<访问修饰符>class 派生类名：基类名
public class Student : Person
{
    private string _Class;

    public string Class
    {
        get { return _Class; }
        set { _Class = value; }
    }

    /// <summary>
    /// 无参构造函数
    /// </summary>
    /// <param name="id"></param>
    /// <param name="Class"></param>
    public Student()
    {

    }

    public string GetClass()
    {
        return Class;
    }
}

public class NewStudent:Student
{
    /// <summary>
    /// 无参构造函数
    /// </summary>
    /// <param name="id"></param>
    /// <param name="Class"></param>
    public NewStudent()
    {
    }

    private string _NID;
    public string NID;

    public string GetNID()
    {
        return NID;
    }
}

    protected void Page_Load(object sender, EventArgs e)
    {
        Person p = new Person("ID1111111");
        Student s = new Student();
        NewStudent n = new NewStudent();

        s.id = "ID2222222";
        s.Class = "12班";

        n.NID = "NID3333333";
        n.id = "ID3333333";
        n.Class = "13班";
        Label1.Text = p.GetID();
        Label2.Text = s.GetID()+s.GetClass();
        Label3.Text = n.GetID() + s.GetClass() + n.GetNID();

        //输出结果 ID1111111111 ID222222212班 ID333333312班NID3333333
    }

    }

    private string _id;
    public string id
    {
        get { return _id; }
        set { _id = value; }
    }

    /// <summary>
    /// 构造函数
    /// </summary>
    /// <param name="id"></param>
    public Person(string id)
    {
        _id = id;
    }

    /// <summary>
    /// 无参构造函数
    /// </summary>
    /// <param name="id"></param>
    /// <param name="Class"></param>
    public Person()
    {
    }

    public virtual string GetID()
    {
        return "虚方法可覆盖";
    }

    public virtual string GetID1()
    {
        return "虚方法可覆盖";
    }

    public string GetID2()
    {
        return "一般的方法，在派生类重写，需要用new";
    }

    public abstract string GetID3(); //抽象方法，不含主体 派生类必须继承此方法
}

//<访问修饰符>class 派生类名：基类名
public class Student : Person
{
    private string _Class;

    public string Class
    {
        get { return _Class; }
        set { _Class = value; }
    }

    public Student()
    {
    }

    public Student(string id):base(id) //调用基类的构造函数
    {

    }

    public override string GetID()
    {
        return "虚方法可覆盖-用override";
    }

    public new string GetID2()
    {
        return "普通方法可覆盖-用new";
    }
    public override string GetID3()
    {
        return "抽象方法必须实现-用override";
    }

}

    protected void Page_Load(object sender, EventArgs e)
    {
        var a = new Student();
        Label1.Text = a.GetID() ;
        Label2.Text = a.GetID1();
        Label3.Text = a.GetID2();
        Label4.Text = a.GetID3();
        //运行结果
        //虚方法可覆盖-用override 虚方法可覆盖 普通方法可覆盖-用new 抽象方法必须实现-用override

    }