using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        List<Person> list = new List<Person>();
        list.Add(new Person("AA", 50));
        list.Add(new Person("BB", 20));
        list.Add(new Person("CC", 30));
        list.Add(new Person("DD", 70));
        Comparison<Person> comparison = new Comparison<Person>
             ((Person x, Person y) =>
             {
                 if (x.Old < y.Old)
                     return -1;
                 else if (x.Old == y.Old)
                     return 0;
                 else
                     return 1;
             });
        list.Sort(comparison);//1、Comparison<Person>
        list.Sort(new Person().Compare);//2、IComparer<Person>
        list.Sort();//3、IComparable
        Console.ReadKey();
    }
}

class Person : IComparable, IComparer<Person>
{
    string name;

    public Person()
    {

    }

    public Person(string name, int old)
    {
        this.name = name;
        this.old = old;
    }

    public string Name
    {
        get { return name; }
        set { name = value; }
    }
    int old;

    public int Old
    {
        get { return old; }
        set { old = value; }
    }

    public int CompareTo(Object o)
    {
        if (this.old > ((Person)o).old)
            return 1;
        else if (this.old == ((Person)o).old)
            return 0;
        else
            return -1;
    }

    public int Compare(Person x, Person y)
    {
        if (x.old < y.old)
            return -1;
        else if (x.old == y.old)
            return 0;
        else
            return 1;
    }
}