模板方法模式 模板方法（英語：template method），是一種行为型软件设计模式。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。 模板方法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，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，或者是只有空体的钩子方法。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）。 用法模板方法模式多用在：
结构 在上面的UML类图中，
用例C++下面是C++的例子：  #include <iostream>
#include <memory>
class View { // AbstractClass
public:
// defines abstract primitive operations that concrete subclasses define to implement steps of an algorithm.
virtual void doDisplay() {}
// implements a template method defining the skeleton of an algorithm.
// The template method calls primitive operations as well as operations defined in AbstractClass or those of other objects.
void display() {
setFocus();
doDisplay();
resetFocus();
}
virtual ~View() = default;
private:
void setFocus() {
std::cout << "View::setFocus\n";
}
void resetFocus() {
std::cout << "View::resetFocus\n";
}
};
class MyView : public View { // ConcreteClass
// implements the primitive operations to carry out subclass-specific steps of the algorithm.
void doDisplay() override {
// render the view's contents
std::cout << "MyView::doDisplay\n";
}
};
int main() {
// The smart pointers prevent memory leaks
std::unique_ptr<View> myview = std::make_unique<MyView>();
myview->display();
}
这个程序的输出为： View::setFocus
MyView::doDisplay
View::resetFocus
Python下面是Python的例子： from abc import ABC, abstractmethod
class View(ABC):
@abstractmethod
def do_display(self): pass
def display(self):
self.__set_focus()
self.do_display()
self.__reset_focus()
def __set_focus(self):
print("View: set focus")
def __reset_focus(self):
print("View: reset focus")
class MyView(View):
def do_display(self):
print("View: do display")
其执行： >>> view = MyView()
>>> view.display()
View: set focus
View: do display
View: reset focus
Java下面是Java的例子： /**
* 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 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
}
}
引用
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