模板方法

模板方法模型是一種行為設計模型和设计模式。模板方法（template method）是一個定義在父類別的方法，负责处理流程、算法的不变部分。模板方法會调用多個定義在父類別的其他工具方法（helper method），而這些方法是算法的可变部分，有可能只是抽象方法並沒有實作。模板方法僅決定這些抽象方法的執行順序，這些抽象方法由子類別負責實作，並且子類別不允許覆盖模板方法（即不能重写处理流程）。

模板方法模式：UML類圖

这种设计模式是一种控制反转的实现方式。因为高层代码不再确定（控制）算法的处理流程。

用法

模板方法模式多用在：

某些類別的演算法中，實做了相同的方法，造成程式碼的重複。
控制子類別必須遵守的一些事項。
...

用例（Java）

 /**
  * An abstract class that is common to several games in
  * which players play against the others, but only one is
  * playing at a given time.
  */
 
 abstract class Game {
 
     private int playersCount;
 
     abstract void initializeGame();
 
     abstract void makePlay(int player);
 
     abstract boolean endOfGame();
 
     abstract void printWinner();
 
     /* A template method : */
     final void playOneGame(int playersCount) {
         this.playersCount = playersCount;
         initializeGame();
         int j = 0;
         while (!endOfGame()){
             makePlay(j);
             j = (j + 1) % playersCount;
         }
         printWinner();
     }
 }

//Now we can extend this class in order to implement actual games:

 class Monopoly extends Game {
 
     /* Implementation of necessary concrete methods */
 
     void initializeGame() {
         // ...
     }
 
     void makePlay(int player) {
         // ...
     }
 
     boolean endOfGame() {
         // ...
     }
 
     void printWinner() {
         // ...
     }
  
     /* Specific declarations for the Monopoly game. */
 
     // ...
 
 }

 class Chess extends Game {
 
     /* Implementation of necessary concrete methods */
 
     void initializeGame() {
         // ...
     }
 
     void makePlay(int player) {
         // ...
     }
 
     boolean endOfGame() {
         // ...
     }
 
     void printWinner() {
         // ...
     }
  
     /* Specific declarations for the chess game. */
 
     // ...
 
 }

 public class Player {
     public static void main(String[] args) {
         Game chessGame = new Chess();
         chessGame.initializeGame();
         chessGame.playOneGame(1); //call template method
     }
 }

C++ 例子

#include<iostream>

// abstract
class BaseClass { 
protected:
	virtual void someMethod() = 0;
public:
	void ThisIsTemplateMethod() { someMethod(); }
};

class ExtendedClass_one : public BaseClass {
protected:
	void someMethod() override {
		puts("[ExtendedClass_one] Re-Define method here.");
	}
};
class ExtendedClass_two : public BaseClass {
protected:
	void someMethod() override {
		puts("[ExtendedClass_two] Re-Define method here.");
	}
};

int main() {

	BaseClass* one = new ExtendedClass_one;
	one->ThisIsTemplateMethod();

	BaseClass* two = new ExtendedClass_two;
	two->ThisIsTemplateMethod();

	return 0;
}

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