C# 语言的高级应用

1、属性

例1：属性概念的引入（问题）

public class Animal
{public int Age;public double Weight;public bool Sex;public Animal(int age, double weight, bool sex){Age = age;Weight = weight;Sex = sex;}public void Eat(){Console.WriteLine("Animal Eat.");}public void Sleep(){Console.WriteLine("Animal Sleep.");}public override string ToString(){return string.Format("Animal Age:{0}, Weight:{1}, Sex:{2}", Age, Weight, Sex);}
}

class Program
{static void Main(string[] args){Animal al = new Animal(1, 1.2, false);Console.WriteLine("Animal Age:{0}, Weight:{1}, Sex:{2}", al.Age, al.Weight, al.Sex);al.Age = -1;al.Weight = -0.5;Console.WriteLine(al);}
}

例2：问题的解决（Java语言解决该问题的方案）

public class Animal
{private int _age;private double _weight;private readonly bool _sex;public int GetAge(){return _age;}public void SetAge(int value){_age = (value > 0) ? value : 0;}public double GetWeight(){return _weight;}public void SetWeight(double value){_weight = (value > 0) ? value : 0;}public bool GetSex(){return _sex;}public Animal(int age, double weight, bool sex){_age = (age > 0) ? age : 0;_weight = (weight > 0) ? weight : 0;_sex = sex;}public void Eat(){Console.WriteLine("Animal Eat.");}public void Sleep(){Console.WriteLine("Animal Sleep.");}public override string ToString(){return string.Format("Animal Age:{0}, Weight:{1}, Sex:{2}", _age, _weight, _sex);}
}

class Program
{static void Main(string[] args){Animal al = new Animal(1, 1.2, false);Console.WriteLine("Animal Age:{0},Weight:{1},Sex:{2}", al.GetAge(), al.GetWeight(), al.GetSex());al.SetAge(-1);al.SetWeight(-0.5);Console.WriteLine(al);}
}

例3：属性的提出

public class Animal
{private int _age;private double _weight;private readonly bool _sex;public int Age{get { return _age; }set { _age = (value > 0) ? value : 0; }}public double Weight{get { return _weight; }set { _weight = (value > 0) ? value : 0; }}public bool Sex{get { return _sex; }}public Animal(int age, double weight, bool sex){_age = (age > 0) ? age : 0;_weight = (weight > 0) ? weight : 0;_sex = sex;}public void Eat(){Console.WriteLine("Animal Eat.");}public void Sleep(){Console.WriteLine("Animal Sleep.");}public override string ToString(){return string.Format("Animal Age:{0}, Weight:{1}, Sex:{2}", Age, Weight, Sex);}
}

class Program
{static void Main(string[] args){Animal al = new Animal(1, 1.2, false);Console.WriteLine("Animal Age:{0}, Weight:{1}, Sex:{2}", al.Age, al.Weight, al.Sex);al.Age = -1;al.Weight = -0.5;Console.WriteLine(al);}
}

说明：C#在声明data时就可以定义set、get方法。

get：定义读取操作。
set：定义赋值操作，value表示传入的参数值。

例4：属性的简化

public class Animal
{private int _age;private double _weight;public int Age{get { return _age; }set { _age = (value > 0) ? value : 0; }}public double Weight{get { return _weight; }set { _weight = (value > 0) ? value : 0; }}public bool Sex { get; private set; }public Animal(int age, double weight, bool sex){_age = (age > 0) ? age : 0;_weight = (weight > 0) ? weight : 0;Sex = sex;}public void Eat(){Console.WriteLine("Animal Eat.");}public void Sleep(){Console.WriteLine("Animal Sleep.");}public override string ToString(){return string.Format("Animal Age:{0},Weight:{1},Sex:{2}", Age, Weight, Sex);}
}

class Program
{static void Main(string[] args){Animal al = new Animal(1, 1.2, false);Console.WriteLine("Animal Age:{0}, Weight:{1}, Sex:{2}", al.Age, al.Weight, al.Sex);al.Age = -1;al.Weight = -0.5;Console.WriteLine(al);}
}

说明：属性可以看作是对私有数据部分增加的一层隔离。

2、索引器

2.1 定义

是集合类中的一种特殊属性，可使得集合类中的元素像数组元素一样访问。

2.2 语法结构

public 元素类型 this[int index]
{get { ... }set { ... }
}public 元素类型 this[string name]
{get { ... }set { ... }
}

例5：利用索引器实现对集合类StudentSet中元素Student的访问。

public class Student
{private string _name;public string Name{get { return _name; }set{_name = string.IsNullOrEmpty(value)? "NULL": value;}}public long ID { get; set; }public Student(long id, string name){ID = id;_name = name;}public override string ToString(){return string.Format("ID:{0},Name:{1}", ID, Name);}
}

public class StudentSet
{private readonly int _maxCount = 500;private readonly Student[] _stus;public int Count{get; private set;}public StudentSet(){Count = 0;_stus = new Student[_maxCount];}public void Add(Student stu){if (stu == null)throw new ArgumentNullException();if (Count == _maxCount)throw new IndexOutOfRangeException();_stus[Count] = stu;Count++;}public Student this[int index]{get{if (index < 0 || index > Count - 1)throw new IndexOutOfRangeException();return _stus[index];}set{if (index < 0 || index > Count - 1)throw new IndexOutOfRangeException();if (value == null)throw new ArgumentNullException();_stus[index] = value;}}
}

class Program
{static void Main(string[] args){StudentSet stuSet = new StudentSet();stuSet.Add(new Student(10086, "张三"));stuSet.Add(new Student(95988, "李四"));stuSet[1].Name = string.Empty;Console.WriteLine(stuSet.Count); Console.WriteLine(stuSet[0]); Console.WriteLine(stuSet[1]); Console.WriteLine(stuSet[2]);//未处理的异常:  System.IndexOutOfRangeException: 索引超出了数组界限。}
}

3、接口

3.1 概念

接口是类设计的蓝图，即只提供声明而没有实现。
接口不可以直接实例化对象（与抽象类相同）。
C#允许一个类实现多个接口（注意与继承的区别）。
接口就是包含一系列不被实现的方法，而把这些方法的实现交给继承它的类。

3.2 表示

例6：根据类图利用Dog实现IAnimal接口

public interface IAnimal
{int Age { get; set; }double Weight { get; set; }void Eat();void Sleep();
}

public class Dog : IAnimal
{private int _age;private double _weight;public int Age{get { return _age; }set { _age = (value >= 0) ? value : 0; }}public double Weight{get { return _weight; }set { _weight = (value >= 0) ? value : 0; }}public void Eat(){Console.WriteLine("Dog Eat");}public void Sleep(){Console.WriteLine("Dog Sleep");}
}

class Program
{static void Main(string[] args){IAnimal al = new Dog();al.Age = 1;al.Weight = 2.5;Console.WriteLine("Dog:Age={0}, Weight={1}", al.Age, al.Weight);al.Eat();al.Sleep();}
}

例7：利用接口实现“饲养系统”

某饲养员（Raiser）在目前状态下需要饲养三种动物：狗（Dog）、鸟（Bird）和鱼（Fish），该三种动物只需要让其睡觉（Sleep）和吃饭（Eat）即可。请设计该饲养系统，要求满足软件设计的“开闭原则”。

方案一：（在抽象类部分已经给出）

方案二：

public interface IAnimal
{int Age { get; set; }double Weight { get; set; }void Eat();void Sleep();
}

public class Bird : IAnimal
{private int _age;private double _weight;public int Age{get { return _age; }set { _age = (value >= 0) ? value : 0; }}public double Weight{get { return _weight; }set { _weight = (value >= 0) ? value : 0; }}public void Eat(){Console.WriteLine("Bird Eat.");}public void Sleep(){Console.WriteLine("Bird Sleep.");}public void Fly(){Console.WriteLine("Bird Fly.");}
}

public class Dog : IAnimal
{private int _age;private double _weight;public int Age{get { return _age; }set { _age = (value >= 0) ? value : 0; }}public double Weight{get { return _weight; }set { _weight = (value >= 0) ? value : 0; }}public void Eat(){Console.WriteLine("Dog Eat.");}public void Sleep(){Console.WriteLine("Dog Sleep.");}public void Run(){Console.WriteLine("Dog Run.");}
}

public class Fish : IAnimal
{private int _age;private double _weight;public int Age{get { return _age; }set { _age = (value >= 0) ? value : 0; }}public double Weight{get { return _weight; }set { _weight = (value >= 0) ? value : 0; }}public void Eat(){Console.WriteLine("Fish Eat.");}public void Sleep(){Console.WriteLine("Fish Sleep.");}public void Swim(){Console.WriteLine("Fish Swim.");}
}

public class Raiser
{public void Raise(IAnimal al){al.Eat();al.Sleep();}
}

class Program
{static void Main(string[] args){Raiser rsr = new Raiser();rsr.Raise(new Dog());rsr.Raise(new Bird());rsr.Raise(new Fish());}
}

3.3 接口（interface）与抽象类（abstract class）

（1）相同点：

接口与抽象类都不可以直接实例化对象。

（2）不同点：

抽象类中的数据和操作必须有限制修饰符，而接口中的数据和操作不可以有限制修饰符。
抽象类中可以有带实现体的方法（非abstract方法），而接口只能有方法的声明。
抽象类在子类中通过override关键字覆写抽象方法，而接口被子类直接实现。

例8：一个类可以实现多个接口，但要注意多个接口中有重名方法的处理。

方式一：

public interface IHighWayWorker
{void HighWayOperation();void Build();
}

public interface IRailWayWorker
{void RailWayOperation();void Build();
}

public class Worker : IRailWayWorker, IHighWayWorker
{public void HighWayOperation(){Console.WriteLine("HighWayOperation.");}public void RailWayOperation(){Console.WriteLine("RailWayOperation");}public void Build(){Console.WriteLine("HighWay,RailWay,Build.");}
}

class Program
{static void Main(string[] args){Worker wr = new Worker();wr.Build(); // HighWay,RailWay,Build.IHighWayWorker hwr = new Worker();hwr.Build(); // HighWay,RailWay,Build.hwr.HighWayOperation(); // HighWayOperation.IRailWayWorker rwr = new Worker();rwr.Build(); // HighWay,RailWay,Build.rwr.RailWayOperation();// RailWayOperation}
}

方式二：

public interface IHighWayWorker
{void HighWayOperation();void Build();
}

public interface IRailWayWorker
{void RailWayOperation();void Build();
}

public class Worker : IHighWayWorker, IRailWayWorker
{public void HighWayOperation(){Console.WriteLine("HighWayOperation.");}public void RailWayOperation(){Console.WriteLine("RailWayOperation");}void IHighWayWorker.Build(){Console.WriteLine("HighWay Build.");}void IRailWayWorker.Build(){Console.WriteLine("RailWay Build.");}// 注意：void IHighWayWorker.Build()和void IRailWayWorker.Build()// 前面不能够加限制修饰符。
}

class Program
{static void Main(string[] args){Worker wr = new Worker();//wr.Build(); 该语句错误IHighWayWorker hwr = new Worker();hwr.Build();//HighWay Build.hwr.HighWayOperation();//HighWayOperation.IRailWayWorker rwr = new Worker();rwr.Build();//RailWay Build.rwr.RailWayOperation();//RailWayOperation}
}

4、泛型

例9：存储int数据类型的集合及操作。

public class IntSet
{private readonly int _maxSize;private readonly int[] _set;public IntSet(){_maxSize = 100;_set = new int[_maxSize];//...}public void Insert(int k, int x){//...._set[k] = x;}public int Locate(int k){//...return _set[k];}
}

class Program
{static void Main(string[] args){IntSet iSet = new IntSet();iSet.Insert(0, 123);int i = iSet.Locate(0);Console.WriteLine(i); // 123}
}

例10：存储string数据类型的集合及操作。

public class StringSet
{private readonly int _maxSize;private readonly string[] _set;public StringSet(){_maxSize = 100;_set = new string[_maxSize];//...}public void Insert(int k, string x){//...._set[k] = x;}public string Locate(int k){//...return _set[k];}
}

class Program
{static void Main(string[] args){StringSet strSet = new StringSet();strSet.Insert(0, "abc");string j = strSet.Locate(0);Console.WriteLine(j); // abc}
}

例11：利用object类存储通用数据类型的集合及操作。

public class GSet
{private readonly int maxSize;private readonly object[] _set;public GSet(){maxSize = 100;_set = new object[maxSize];//...}public void Insert(int k, object x){//...._set[k] = x;}public object Locate(int k){//...return _set[k];}
}

class Program
{static void Main(string[] args){GSet gSet1 = new GSet();gSet1.Insert(0, 123);int k1 = (int)gSet1.Locate(0);Console.WriteLine(k1); // 123GSet gSet2 = new GSet();gSet2.Insert(0, "abc");string k2 = (string)gSet2.Locate(0);Console.WriteLine(k2); // abcGSet gSet3 = new GSet();gSet3.Insert(0, 123);gSet3.Insert(1, "abc");//编译时可以通过，运行时出现异常。int k3 = (int)gSet3.Locate(1); //这样使用存在类型安全问题。Console.WriteLine(k3);// 未处理的异常:  System.InvalidCastException: 指定的转换无效。}
}

泛型定义：即参数化类型。

在编译时用一个具体类型代替该参数类型，可定义类型安全的类而不影响工作效率。

例12：利用泛型T存储通用数据类型的集合及操作。

public class GSet<T>
{private readonly int _maxSize;private readonly T[] _set;public GSet(){_maxSize = 100;_set = new T[_maxSize];//...}public void Insert(int k, T x){//...._set[k] = x;}public T Locate(int k){//...return _set[k];}
}

class Program
{static void Main(string[] args){GSet<int> gSet1 = new GSet<int>();gSet1.Insert(0, 123);int k1 = gSet1.Locate(0);Console.WriteLine(k1); // 123GSet<string> gSet2 = new GSet<string>();gSet2.Insert(0, "abc");string k2 = gSet2.Locate(0);Console.WriteLine(k2); // abc}
}

我们把T称为类型参数，当然我们也可以对T进行约束。

例13：为类型参数T增加约束，比如T只能是值类型。

public class GSet<T> where T : struct
{private readonly int _maxSize;private readonly T[] _set;public GSet(){_maxSize = 100;_set = new T[_maxSize];//...}public void Insert(int k, T x){//...._set[k] = x;}public T Locate(int k){//...return _set[k];}
}

class Program
{static void Main(string[] args){GSet<int> gSet1 = new GSet<int>();gSet1.Insert(0, 123);int k1 = gSet1.Locate(0);Console.WriteLine(k1); // 123// GSet<string> gSet2 = new GSet<string>(); // 编译错误// 错误 CS0453 类型“string”必须是不可以为 null 值的类型，// 才能用作泛型类型或方法“GSet < T >”中的参数“T” }
}

有关泛型约束可以查看以下图文：

技术图文：C#语言中的泛型 I
技术图文：C#语言中的泛型 II

5、类与类之间的关系

public class Oxygen
{//...
}

public class Water
{//...
}

public abstract class Animal
{public int Age;public double Weight;public abstract void Eat();public abstract void Sleep();public abstract void Breed();public abstract void Metabolism(Oxygen o2, Water water);
}

public class Bird : Animal
{public string Feather;public void Fly(){//...}public void Egg(){//...}public override void Eat(){//...}public override void Sleep(){//...}public override void Breed(){//...}public override void Metabolism(Oxygen o2, Water water){//...}
}

public class Penguin : Bird
{//...
}

public class Goose : Bird
{//...
}

public class Duck : Bird
{//...
}

public class Climate
{//...
}

public class Penguin : Bird
{private Climate _climate;//...
}

public interface ILanguage
{void Speak();
}

public class DonaldDuck : Duck, ILanguage
{public void Speak(){//...}//...
}