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
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1 class Program 2 { 3 static void Main(string[] args) 4 { 5 Person person1 = new Chiness("吉米"); 6 Person person2 = new Japanese("山本"); 7 person1.SayHello(); 8 person2.SayHello(); 9 } 10 } 11 public class Person 12 { 13 public string Name { set; get; } 14 public Person(string name) 15 { 16 this.Name = name; 17 } 18 public virtual void SayHello() 19 { 20 Console.WriteLine("I'm Person,my name is " + this.Name); 21 } 22 } 23 public class Chiness : Person 24 { 25 public Chiness(string name) 26 : base(name) 27 { 28 29 } 30 public override void SayHello() 31 { 32 Console.WriteLine("I'm Chiness,my name is " + this.Name); 33 } 34 } 35 public class Japanese : Person 36 { 37 public Japanese(string name) 38 : base(name) 39 { 40 41 } 42 public new void SayHello() 43 { 44 Console.WriteLine("I'm Japanese,my name is " + this.Name); 45 } 46 }
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二、装箱和拆箱
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1 class Program 2 { 3 static void Main(string[] args) 4 { 5 ArrayList listArr = new ArrayList(); 6 List<object> list = new List<object>(); 7 Stopwatch sw = new Stopwatch(); 8 sw.Start(); 9 int k = 10; 10 for (int i = 0; i < 10000000; i++) 11 { 12 object kk = k; 13 list.Add(kk); 14 } 15 //装箱:00:00:00.9023259 16 //拆箱:00:00:00.0885700 17 sw.Stop(); 18 Console.WriteLine(sw.Elapsed); 19 Console.ReadKey(); 20 } 21 }
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
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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!!!
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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; } } }