192 lines
3.1 KiB
Markdown
192 lines
3.1 KiB
Markdown
# 第六课：继承和接口
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## 继承（Inheritance）
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子类继承父类的属性和方法，避免重复代码。
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```csharp
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// 父类
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class Animal
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{
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public string name;
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public void Eat()
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{
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Console.WriteLine($"{name} 在吃东西");
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}
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}
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// 子类
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class Dog : Animal
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{
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public void Bark()
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{
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Console.WriteLine($"{name} 在叫: 汪汪!");
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}
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}
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```
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```csharp
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Dog dog = new Dog();
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dog.name = "旺财";
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dog.Eat(); // 继承自 Animal
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dog.Bark(); // 自己独有的
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```
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## 方法重写（override）
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```csharp
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// 父类 virtual 方法
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class Animal
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{
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public string name;
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public virtual void Speak()
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{
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Console.WriteLine($"{name} 发出了声音");
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}
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}
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// 子类重写
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class Cat : Animal
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{
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public override void Speak()
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{
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Console.WriteLine($"{name} 喵喵喵~");
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}
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}
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```
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```csharp
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Animal a = new Cat();
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a.name = "小猫";
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a.Speak(); // 输出: 小猫 喵喵喵~
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```
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## base 关键字
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子类调用父类的方法/构造函数：
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```csharp
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class Dog : Animal
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{
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public string breed;
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public Dog(string name, string breed) : base(name)
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{
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this.breed = breed;
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}
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public override void Speak()
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{
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base.Speak(); // 先调用父类方法
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Console.WriteLine($"{name} 汪汪!");
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}
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}
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```
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## 访问修饰符 protected
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| 修饰符 | 任何地方 | 继承访问 |
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|--------|----------|----------|
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| `private` | ✗ | ✗ |
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| `protected` | ✗ | ✓ |
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```csharp
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class Animal
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{
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protected string name; // private 的话子类也访问不到
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}
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class Dog : Animal
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{
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public void Test()
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{
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name = "旺财"; // protected 可以访问
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}
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}
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```
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## 接口（Interface）
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接口 = 约定/契约，定义必须实现的方法。
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```csharp
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// 定义接口
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interface IFlyable
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{
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void Fly(); // 不写实现
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int MaxAltitude { get; } // 可以有属性
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}
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// 实现接口
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class Bird : IFlyable
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{
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public int MaxAltitude => 1000;
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public void Fly()
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{
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Console.WriteLine("鸟儿在飞翔");
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}
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}
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class Plane : IFlyable
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{
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public int MaxAltitude => 10000;
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public void Fly()
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{
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Console.WriteLine("飞机在飞翔");
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}
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}
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```
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## 接口 vs 继承
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| | 继承 | 接口 |
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|---|---|---|
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| 关键词 | `class A : B` | `class A : IB` |
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| 只能继承一个父类 | ✓ | 可以实现多个接口 |
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| 继承获得代码 | ✓ | 只获得"约定" |
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| 何时用 | 代码复用 | 约定行为 |
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```csharp
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// 一个类只能继承一个父类
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class Dog : Animal { }
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// 但可以实现多个接口
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class Duck : Animal, IFlyable, ISwimable
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{
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public void Fly() { }
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public void Swim() { }
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}
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```
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## 例子：设备驱动架构
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```csharp
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// 设备接口
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interface IDevice
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{
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void Connect();
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void Disconnect();
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bool IsConnected { get; }
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}
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// 麦克风设备
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class Microphone : IDevice
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{
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public bool IsConnected { get; private set; }
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public void Connect()
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{
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Console.WriteLine("麦克风连接");
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IsConnected = true;
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}
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public void Disconnect()
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{
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Console.WriteLine("麦克风断开");
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IsConnected = false;
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}
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}
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```
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