C# 面向对象实例演示

C# 面向对象编程实例演示

一、基础概念回顾

面向对象编程(OOP)的四大基本特性：

1. ​​封装​​ - 将数据和操作数据的方法绑定在一起
2. ​​继承​​ - 创建新类时重用现有类的属性和方法
3. ​​多态​​ - 同一操作作用于不同对象产生不同结果
4. ​​抽象​​ - 简化复杂系统，只暴露必要接口

二、完整实例演示

示例1：银行账户系统

using System;// 抽象基类 - 封装共同属性和行为
public abstract class BankAccount
{// 封装字段private string _accountNumber;private decimal _balance;// 属性 - 控制对字段的访问public string AccountNumber { get => _accountNumber; private set => _accountNumber = value; }public decimal Balance { get => _balance; protected set => _balance = value; }// 构造函数protected BankAccount(string accountNumber, decimal initialBalance){AccountNumber = accountNumber;Balance = initialBalance;}// 抽象方法 - 由子类实现public abstract void Deposit(decimal amount);public abstract void Withdraw(decimal amount);// 虚方法 - 可被子类重写public virtual void DisplayAccountInfo(){Console.WriteLine($"账户号: {AccountNumber}");Console.WriteLine($"余额: {Balance:C}");}
}// 派生类 - 继承并扩展功能
public class SavingsAccount : BankAccount
{private const decimal MinimumBalance = 100;private const decimal InterestRate = 0.02m;public SavingsAccount(string accountNumber, decimal initialBalance) : base(accountNumber, initialBalance){if (initialBalance < MinimumBalance)throw new ArgumentException("储蓄账户最低余额为100元");}// 实现抽象方法public override void Deposit(decimal amount){if (amount <= 0)throw new ArgumentException("存款金额必须大于0");Balance += amount;Console.WriteLine($"成功存入 {amount:C}，当前余额: {Balance:C}");}public override void Withdraw(decimal amount){if (amount <= 0)throw new ArgumentException("取款金额必须大于0");if (Balance - amount < MinimumBalance)throw new InvalidOperationException("取款后余额不能低于最低限额");Balance -= amount;Console.WriteLine($"成功取出 {amount:C}，当前余额: {Balance:C}");}// 新增方法public void ApplyInterest(){decimal interest = Balance * InterestRate;Balance += interest;Console.WriteLine($"利息已应用: {interest:C}，新余额: {Balance:C}");}// 重写虚方法public override void DisplayAccountInfo(){base.DisplayAccountInfo();Console.WriteLine($"账户类型: 储蓄账户");Console.WriteLine($"最低余额要求: {MinimumBalance:C}");}
}// 另一个派生类
public class CheckingAccount : BankAccount
{private const decimal OverdraftLimit = -500;public CheckingAccount(string accountNumber, decimal initialBalance) : base(accountNumber, initialBalance){}public override void Deposit(decimal amount){if (amount <= 0)throw new ArgumentException("存款金额必须大于0");Balance += amount;Console.WriteLine($"支票账户存入 {amount:C}，当前余额: {Balance:C}");}public override void Withdraw(decimal amount){if (amount <= 0)throw new ArgumentException("取款金额必须大于0");if (Balance - amount < OverdraftLimit)throw new InvalidOperationException($"取款后余额不能低于透支限额 {OverdraftLimit:C}");Balance -= amount;Console.WriteLine($"支票账户取出 {amount:C}，当前余额: {Balance:C}");}public void WriteCheck(decimal amount){try{Withdraw(amount);Console.WriteLine($"已开具 {amount:C} 支票");}catch (Exception ex){Console.WriteLine($"开具支票失败: {ex.Message}");}}
}// 演示类
public class BankDemo
{public static void Main(){// 多态 - 使用基类引用指向派生类对象BankAccount savings = new SavingsAccount("SAV12345", 1000);BankAccount checking = new CheckingAccount("CHK67890", 500);// 调用方法savings.Deposit(200);savings.Withdraw(50);savings.DisplayAccountInfo();Console.WriteLine("\n-----------------\n");checking.Deposit(300);checking.WriteCheck(100);checking.Withdraw(700); // 尝试透支checking.DisplayAccountInfo();// 使用is和as运算符if (savings is SavingsAccount savingsAcc){savingsAcc.ApplyInterest();}BankAccount? unknownAccount = null;var tempAccount = unknownAccount as SavingsAccount;if (tempAccount == null){Console.WriteLine("账户类型转换失败");}}
}

示例2：图形计算系统

using System;
using System.Collections.Generic;// 接口定义
public interface IShape
{decimal CalculateArea();decimal CalculatePerimeter();void Draw();
}// 具体实现类
public class Circle : IShape
{private decimal _radius;public Circle(decimal radius){if (radius <= 0)throw new ArgumentException("半径必须大于0");_radius = radius;}public decimal Radius => _radius;public decimal CalculateArea() => (decimal)Math.PI * _radius * _radius;public decimal CalculatePerimeter() => 2 * (decimal)Math.PI * _radius;public void Draw(){Console.WriteLine($"绘制圆形，半径: {_radius}");// 实际绘图代码...}
}public class Rectangle : IShape
{private decimal _width;private decimal _height;public Rectangle(decimal width, decimal height){if (width <= 0 || height <= 0)throw new ArgumentException("宽度和高度必须大于0");_width = width;_height = height;}public decimal Width => _width;public decimal Height => _height;public decimal CalculateArea() => _width * _height;public decimal CalculatePerimeter() => 2 * (_width + _height);public void Draw(){Console.WriteLine($"绘制矩形，宽度: {_width}，高度: {_height}");// 实际绘图代码...}
}// 工厂类 - 封装对象创建逻辑
public static class ShapeFactory
{public static IShape CreateShape(string shapeType, params decimal[] parameters){return shapeType.ToLower() switch{"circle" => new Circle(parameters[0]),"rectangle" => new Rectangle(parameters[0], parameters[1]),_ => throw new ArgumentException("未知的形状类型")};}
}// 图形管理器 - 组合多个图形
public class ShapeManager
{private readonly List<IShape> _shapes = new();public void AddShape(IShape shape){_shapes.Add(shape);}public decimal TotalArea() => _shapes.Sum(s => s.CalculateArea());public decimal TotalPerimeter() => _shapes.Sum(s => s.CalculatePerimeter());public void DrawAllShapes(){foreach (var shape in _shapes){shape.Draw();}}
}// 演示类
public class ShapeDemo
{public static void Main(){// 多态使用IShape circle = new Circle(5);IShape rectangle = new Rectangle(4, 6);Console.WriteLine($"圆形面积: {circle.CalculateArea()}");Console.WriteLine($"矩形周长: {rectangle.CalculatePerimeter()}");// 工厂模式使用IShape anotherCircle = ShapeFactory.CreateShape("circle", 3);IShape anotherRectangle = ShapeFactory.CreateShape("rectangle", 2, 5);// 组合模式使用var manager = new ShapeManager();manager.AddShape(circle);manager.AddShape(rectangle);manager.AddShape(anotherCircle);manager.AddShape(anotherRectangle);Console.WriteLine($"\n所有图形总面积: {manager.TotalArea()}");Console.WriteLine($"所有图形总周长: {manager.TotalPerimeter()}");Console.WriteLine("\n绘制所有图形:");manager.DrawAllShapes();// 接口实现检查if (circle is Circle c){Console.WriteLine($"这是一个圆形，半径: {c.Radius}");}// 使用as运算符var maybeCircle = rectangle as Circle;if (maybeCircle == null){Console.WriteLine("这不是一个圆形");}}
}

示例3：动物模拟系统

using System;// 基类
public abstract class Animal
{// 字段封装private string _name;private int _age;// 属性public string Name { get => _name; set => _name = value ?? throw new ArgumentNullException(nameof(value)); }public int Age { get => _age; protected set => _age = value >= 0 ? value : throw new ArgumentOutOfRangeException(nameof(value)); }// 构造函数protected Animal(string name, int age){Name = name;Age = age;}// 抽象方法 - 必须由子类实现public abstract void MakeSound();// 虚方法 - 可被子类重写public virtual void Eat(){Console.WriteLine($"{Name}正在吃东西");}// 密封方法 - 阻止进一步重写public sealed override string ToString(){return $"{GetType().Name}: {Name}, {Age}岁";}
}// 派生类
public class Dog : Animal
{public Dog(string name, int age) : base(name, age){}public override void MakeSound(){Console.WriteLine($"{Name}汪汪叫!");}// 新增方法public void Fetch(){Console.WriteLine($"{Name}正在捡球");}
}public class Cat : Animal
{public Cat(string name, int age) : base(name, age){}public override void MakeSound(){Console.WriteLine($"{Name}喵喵叫!");}// 重写基类方法public override void Eat(){Console.WriteLine($"{Name}正在优雅地吃猫粮");}// 隐藏基类方法(不推荐)public new void ToString(){Console.WriteLine("这不会覆盖基类的ToString");}
}// 接口
public interface ITrainable
{void Train(string command);
}// 实现接口的类
public class PoliceDog : Dog, ITrainable
{public PoliceDog(string name, int age) : base(name, age){}public void Train(string command){Console.WriteLine($"{Name}正在接受'{command}'训练");}
}// 演示类
public class AnimalDemo
{public static void Main(){// 多态使用Animal[] animals = new Animal[]{new Dog("旺财", 3),new Cat("咪咪", 2),new PoliceDog("阿黄", 5)};foreach (var animal in animals){animal.MakeSound();animal.Eat();// 类型检查与转换if (animal is Dog dog){dog.Fetch();}if (animal is ITrainable trainable){trainable.Train("坐下");}Console.WriteLine(animal.ToString());Console.WriteLine();}// 接口实现检查if (animals[2] is PoliceDog policeDog){policeDog.Train("卧倒");}// as运算符var maybeTrainable = animals[1] as ITrainable;if (maybeTrainable == null){Console.WriteLine("猫不能接受训练");}}
}

三、关键概念详解

1. 封装

​​优点​​：

• 隐藏实现细节
• 提供公共接口
• 控制对数据的访问

​​示例​​：

public class Person
{// 私有字段private string _ssn;// 公共属性 - 控制访问public string SSN{get => _ssn;set{if (string.IsNullOrEmpty(value))throw new ArgumentException("SSN不能为空");if (value.Length != 9)throw new ArgumentException("SSN必须是9位");_ssn = value;}}// 只读属性public int Age { get; private set; }// 构造函数初始化public Person(string ssn, int age){SSN = ssn;Age = age;}// 方法封装行为public void HaveBirthday(){Age++;Console.WriteLine($"生日快乐！现在是{Age}岁");}
}

2. 继承

​​语法​​：

public class BaseClass
{// 基类成员
}public class DerivedClass : BaseClass
{// 派生类成员
}

​​示例​​：

public class Vehicle
{public string Make { get; set; }public string Model { get; set; }public virtual void Start(){Console.WriteLine("车辆启动");}
}public class Car : Vehicle
{public int DoorCount { get; set; }public override void Start(){Console.WriteLine("汽车启动");base.Start(); // 调用基类方法}public void Honk(){Console.WriteLine("喇叭响");}
}

3. 多态

​​实现方式​​：

1. 方法重写(override)
2. 接口实现
3. 抽象方法

​​示例​​：

public interface IShape
{decimal Area();
}public class Circle : IShape
{public decimal Radius { get; set; }public decimal Area() => (decimal)Math.PI * Radius * Radius;
}public class Rectangle : IShape
{public decimal Width { get; set; }public decimal Height { get; set; }public decimal Area() => Width * Height;
}// 使用
IShape[] shapes = new IShape[]
{new Circle { Radius = 5 },new Rectangle { Width = 4, Height = 6 }
};foreach (var shape in shapes)
{Console.WriteLine($"面积: {shape.Area()}");
}

4. 抽象

​​抽象类​​：

public abstract class Animal
{public abstract void MakeSound(); // 必须由子类实现public virtual void Eat() // 可选实现{Console.WriteLine("动物在吃东西");}
}

​​接口​​：

public interface IDriveable
{void Drive();int MaxSpeed { get; set; }
}

​​示例​​：

public abstract class Shape
{public abstract decimal CalculateArea();public virtual void Display(){Console.WriteLine("这是一个形状");}
}public class Triangle : Shape
{public decimal Base { get; set; }public decimal Height { get; set; }public override decimal CalculateArea(){return Base * Height / 2;}public new void Display() // 隐藏基类方法(不推荐){Console.WriteLine("这是一个三角形");}
}

四、设计模式示例

1. 工厂模式

public interface IWeapon
{void Attack();
}public class Sword : IWeapon
{public void Attack() => Console.WriteLine("挥剑攻击");
}public class Bow : IWeapon
{public void Attack() => Console.WriteLine("拉弓射箭");
}public static class WeaponFactory
{public static IWeapon CreateWeapon(string weaponType){return weaponType.ToLower() switch{"sword" => new Sword(),"bow" => new Bow(),_ => throw new ArgumentException("未知武器类型")};}
}// 使用
IWeapon weapon = WeaponFactory.CreateWeapon("sword");
weapon.Attack();

2. 单例模式

public sealed class Logger
{private static readonly Lazy<Logger> _instance = new Lazy<Logger>(() => new Logger());public static Logger Instance => _instance.Value;private Logger() { }public void Log(string message){Console.WriteLine($"[{DateTime.Now}] {message}");}
}// 使用
Logger.Instance.Log("系统启动");

3. 观察者模式

public interface IObserver
{void Update(string message);
}public class NewsAgency
{private readonly List<IObserver> _observers = new();public void AddObserver(IObserver observer){_observers.Add(observer);}public void RemoveObserver(IObserver observer){_observers.Remove(observer);}public void PublishNews(string news){foreach (var observer in _observers){observer.Update(news);}}
}public class Subscriber : IObserver
{public string Name { get; }public Subscriber(string name){Name = name;}public void Update(string message){Console.WriteLine($"{Name}收到新闻: {message}");}
}// 使用
var agency = new NewsAgency();
agency.AddObserver(new Subscriber("张三"));
agency.AddObserver(new Subscriber("李四"));agency.PublishNews("股市今日大涨");

五、最佳实践

1. ​​优先使用组合而非继承​​：

   // 更好的设计 - 使用组合
   public class Engine { }public class Car
   {public Engine Engine { get; } = new Engine();
   }

2. ​​遵循SOLID原则​​：

   • 单一职责原则(SRP)
   • 开闭原则(OCP)
   • 里氏替换原则(LSP)
   • 接口隔离原则(ISP)
   • 依赖倒置原则(DIP)

3. ​​合理使用访问修饰符​​：

   public class MyClass
   {public int PublicField; // 慎用protected int ProtectedField;internal int InternalField;protected internal int ProtectedInternalField;private int _privateField; // 推荐
   }

4. ​​避免过度使用继承​​：

   • 继承层次不要太深(通常不超过3层)
   • 考虑使用接口或组合替代

5. ​​使用属性而非公共字段​​：

   // 不推荐
   public class BadDesign
   {public int Value;
   }// 推荐
   public class GoodDesign
   {private int _value;public int Value{get => _value;set => _value = value > 0 ? value : throw new ArgumentOutOfRangeException();}
   }

6. ​​实现IDisposable接口管理资源​​：

   public class ResourceHolder : IDisposable
   {private bool _disposed = false;private FileStream _fileStream;public ResourceHolder(string path){_fileStream = new FileStream(path, FileMode.Open);}public void Dispose(){Dispose(true);GC.SuppressFinalize(this);}protected virtual void Dispose(bool disposing){if (!_disposed){if (disposing){_fileStream?.Dispose();}_disposed = true;}}~ResourceHolder() => Dispose(false);
   }

通过以上实例和最佳实践，您可以更好地理解和应用C#的面向对象编程特性，编写出更健壮、可维护和可扩展的代码。