模板方法模式，基于继承实现的简单的设计模式（设计模式与开发实践 P11）

模板方法模式是一种基于继承的设计模式，由两部分构成：

• 抽象父类（一般封装了子类的算法框架）
• 具体的实现子类

实现

简单地通过继承就可以实现

举例

足球赛 和 篮球赛 都有 3 个步骤，初始化，开始游戏，结束游戏

我们发现他们都有这个过程，就可以把相同的点提取出来，设置成一个模板！

这里我们举例的 3 个方法都是抽象方法，有时如果子类的行为是一致的，可以直接实现具体方法～

using System;

public abstract class Game
{
    public void Play()
    {
        Initialize();
        StartGame();
        EndGame();
    }

    protected abstract void Initialize();

    protected abstract void StartGame();

    protected abstract void EndGame();
}

public class FootballGame : Game
{
    protected override void Initialize()
    {
        Console.WriteLine("Football game initialized. Setting up teams and players.");
    }

    protected override void StartGame()
    {
        Console.WriteLine("Football game started. Kickoff!");
    }

    protected override void EndGame()
    {
        Console.WriteLine("Football game ended. Final score and statistics displayed.");
    }
}

public class BasketballGame : Game
{
    protected override void Initialize()
    {
        Console.WriteLine("Basketball game initialized. Setting up teams and players.");
    }

    protected override void StartGame()
    {
        Console.WriteLine("Basketball game started. Tip-off!");
    }

    protected override void EndGame()
    {
        Console.WriteLine("Basketball game ended. Final score and statistics displayed.");
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        Game footballGame = new FootballGame();
        footballGame.Play();

        Console.WriteLine();

        Game basketballGame = new BasketballGame();
        basketballGame.Play();
    }
}

应用

常被架构师用来搭建项目的框架，程序员负责往里面填空

比如 Java 程序员经常用 HttpServlet 来开发项目，他包含 7 个生命周期，每个生命周期都对应一个 do 方法，这些方法就需要 HttpServlet 的子类进行 具体实现

钩子 Hook

根据上面的例子，如果有一种非常特别的球赛不需要 Initialize 就可以开始呢？

我们可以在容易变化的方法处设置一个 Hook，他可以有一个默认的实现，需不需要 Hook 挂钩则由子类自行决定，这样程序就有了变化的可能～

using System;

public abstract class Game
{
    public void Play()
    {
        Initialize();
        StartGame();
        EndGame();
    }

    protected virtual void Initialize()
    {
        Console.WriteLine("Game initialized. Setting up teams and players.");
        // 在这里添加挂钩（Hook）行为
        AdditionalInitialization();
    }

    protected abstract void StartGame();

    protected abstract void EndGame();

    protected virtual void AdditionalInitialization()
    {
        // 默认的挂钩行为为空
    }
}

public class FootballGame : Game
{
    protected override void StartGame()
    {
        Console.WriteLine("Football game started. Kickoff!");
    }

    protected override void EndGame()
    {
        Console.WriteLine("Football game ended. Final score and statistics displayed.");
    }

    protected override void AdditionalInitialization()
    {
        Console.WriteLine("Additional initialization for Football game.");
    }
}

public class BasketballGame : Game
{
    protected override void StartGame()
    {
        Console.WriteLine("Basketball game started. Tip-off!");
    }

    protected override void EndGame()
    {
        Console.WriteLine("Basketball game ended. Final score and statistics displayed.");
    }

    protected override void AdditionalInitialization()
    {
        Console.WriteLine("Additional initialization for Basketball game.");
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        Game footballGame = new FootballGame();
        footballGame.Play();

        Console.WriteLine();

        Game basketballGame = new BasketballGame();
        basketballGame.Play();
    }
}