C# 基础

一、多态（virtual，override，new，abstract 关键字）
　　抽象类：abstract必须子类重写，并且不能申明主体
　　 　　　　virtual 可以不重写，编译器会警告，必须申明主体
　　 实现类：override 重写，对应父类的 abstract 和 virtual
　　　　　　 new 对应父类的 virtual
　　override sealed 不允许子类 重写

    class Program
    {
        static void Main(string[] args)
        {
            Person person1 = new Chiness("吉米");
            Person person2 = new Japanese("山本");
            person1.SayHello();
            person2.SayHello();
        }
    }
    public class Person
    {
        public string Name { set; get; }
        public Person(string name)
        {
            this.Name = name;
        }
        public virtual void SayHello()
        {
            Console.WriteLine("I'm Person,my name is " + this.Name);
        }
    }
    public class Chiness : Person
    {
        public Chiness(string name)
            : base(name)
        {

        }
        public override void SayHello()
        {
            Console.WriteLine("I'm Chiness,my name is " + this.Name);
        }
    }
    public class Japanese : Person
    {
        public Japanese(string name)
            : base(name)
        {

        }
        public new void SayHello()
        {
            Console.WriteLine("I'm Japanese,my name is " + this.Name);
        }
    }

  

二、装箱和拆箱

    class Program
    {
        static void Main(string[] args)
        {
            ArrayList listArr = new ArrayList();
            List<object> list = new List<object>();
            Stopwatch sw = new Stopwatch();
            sw.Start();
            int k = 10;
            for (int i = 0; i < 10000000; i++)
            {
                object kk = k;
                list.Add(kk);
            }
            //装箱：00:00:00.9023259
            //拆箱：00:00:00.0885700
            sw.Stop();
            Console.WriteLine(sw.Elapsed);
            Console.ReadKey();
        }
    }

  同样的操作装箱需时间：00:00:00.9023259，拆箱只需00:00:00.0885700

三、委托

using System;

namespace ConsoleApplication1
{
    class Program
    {
        public delegate int dele(string x);
        static void Main(string[] args)
        {
            Action<string> action = str => { Console.WriteLine(str + "1"); Console.WriteLine(str + "2"); };
            action("123");//1231,1232
            Func<string, int> func1 = x => A(x);
            int i = func1("123456");
            Console.WriteLine(i);//16
            Func<string, string, string, string> func2 = (x, y, z) => x + y + z;
            Console.WriteLine(func2("1","2","3"));//123

        }
        public static int A(string a)
        {
            return a.Length + 10;
        }
    }
}

四、Linq 乱 ... 仔细看！！！

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            List<A> list = new List<A>() 
            {
                new A(){Id=1,Name="AA"},
                new A(){Id=6,Name="WW"},
                new A(){Id=4,Name="TT"},
                new A(){Id=7,Name="SS"},
                new A(){Id=5,Name="RR"},
                new A(){Id=2,Name="QQ"},
                new A(){Id=3,Name="GG"},
            };
            //执行
            Action<List<A>> action = x =>
            {
                x.ForEach(item => Console.WriteLine("{0},{1},{2}", item.Id, item.Name, item.Age));
            };
            Action<A> actionSingle = x => Console.WriteLine("{0},{1},{2}", x.Id, x.Name, x.Age);
            var list1 = list;
            //筛选
            var l = list1.Where(n => n.Id > 3);
            //获取，排序 OrderByDescending 降序，OrderBy 升序
            list1 = l.Select(n => n).OrderByDescending(x => x.Id).ToList();
            //action(list1);

            var list2 = list;
            //所有元素都满足返回 true 否则返回 false
            bool b = list2.All(n => n.Age == 1);
            //Console.WriteLine(b);
            //任何一元素满足返回 true 否则返回 false
            b = list2.Any(n => n.Id > 1);
            //获取平均值
            double average = list1.Average(n => n.Id);
            //Console.WriteLine(average);
            list = list.Concat(list).ToList();
            //action(list);
            A a = new A() { Id = 1, Name = "AAA" };
            list.Add(a);
            b = list.Contains(a);
            //Console.WriteLine(b);//true
            int i = list.Count(x => x.Name.Length > 2);
            //Console.WriteLine(i);//1
            //返回 System.Collections.Generic.IEnumerable<T> 类型
            var listAble = list.DefaultIfEmpty();
            list.Add(a);
            //action(list);
            list = list.Distinct().ToList();
            //action(list);

            //First 获取第一个满足条件的数据,不满足条件的报异常
            var listOne = list.First<A>(n => n.Id > 1);
            //FirstOrDefault 不满足条件的报异常的情况 返回null 值
            listOne = list.FirstOrDefault<A>(n => n.Id > 12);
            //actionSingle(listOne);
            // Last 获取最一个满足条件的数据,不满足条件的报异常
            var listLast = list.First<A>(n => n.Id > 12);
            //FirstOrDefault 不满足条件的报异常的情况 返回null 值
            listOne = list.FirstOrDefault<A>(n => n.Id > 12);

            // Union 对两个集合采取“并”操作
            list = list.Union(list).ToList();
            list = list.Union(new List<A>() { new A() { Id = 12, Name = "123465", Age = 122 } }).ToList();
            //action(list);
            //Intersect  对两个集合采取“交”操作
            list = list.Intersect(new List<A>() { new A() { Id = 12, Name = "123465", Age = 122 } }).ToList();
            //action(list);
        }
    }
    public class A
    {
        public int Id { set; get; }
        public string Name { set; get; }
        public int Age { set; get; }
    }
}