设计模式——模板方法模式（Template Method Pattern）

模板方法模式在一个方法中定义一个算法的骨架，而将一些步骤延迟到子类中。模版方法是的子类可以在不改变算法结构的情况下，重新定义算法中的某些步骤。

类图

（图片源于网络）

代码实现（Java）

// CaffeineBeverage.java
public abstract class CaffeineBeverage {
                                                    
    final void prepareRecipe() {
        boilWater();
        brew();
        pourInCup();
        addCondiments();
    }
                                                   
    abstract void brew();
                                                    
    abstract void addCondiments();
                                                   
    void boilWater() {
        System.out.println("Boiling water");
    }
                                                    
    void pourInCup() {
        System.out.println("Pouring into cup");
    }
}

// CaffeineBeverageWithHook.java
public abstract class CaffeineBeverageWithHook {
                                                
    void prepareRecipe() {
        boilWater();
        brew();
        pourInCup();
        if (customerWantsCondiments()) {
            addCondiments();
        }
    }
                                                
    abstract void brew();
                                                
    abstract void addCondiments();
                                                
    void boilWater() {
        System.out.println("Boiling water");
    }
                                                
    void pourInCup() {
        System.out.println("Pouring into cup");
    }
                                                
    boolean customerWantsCondiments() {
        return true;
    }
}

// Coffee.java
public class Coffee extends CaffeineBeverage {
    public void brew() {
        System.out.println("Dripping Coffee through filter");
    }
    public void addCondiments() {
        System.out.println("Adding Sugar and Milk");
    }
}

// CoffeeWithHook.java
public class CoffeeWithHook extends CaffeineBeverageWithHook {
                                          
    public void brew() {
        System.out.println("Dripping Coffee through filter");
    }
                                          
    public void addCondiments() {
        System.out.println("Adding Sugar and Milk");
    }
                                          
    public boolean customerWantsCondiments() {
        String answer = getUserInput();
        if (answer.toLowerCase().startsWith("y")) {
            return true;
        } else {
            return false;
        }
    }
                                          
    private String getUserInput() {
        String answer = null;
        System.out.print("Would you like milk and sugar with your coffee (y/n)? ");
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        try {
            answer = in.readLine();
        } catch (IOException ioe) {
            System.err.println("IO error trying to read your answer");
        }
        if (answer == null) {
            return "no";
        }
        return answer;
    }
}

// Tea.java
public class Tea extends CaffeineBeverage {
    public void brew() {
        System.out.println("Steeping the tea");
    }
    public void addCondiments() {
        System.out.println("Adding Lemon");
    }
}

// TeaWithHook.java
public class TeaWithHook extends CaffeineBeverageWithHook {
                       
    public void brew() {
        System.out.println("Steeping the tea");
    }
                       
    public void addCondiments() {
        System.out.println("Adding Lemon");
    }
                       
    public boolean customerWantsCondiments() {
        String answer = getUserInput();
        if (answer.toLowerCase().startsWith("y")) {
            return true;
        } else {
            return false;
        }
    }
                       
    private String getUserInput() {
        // get the user's response
        String answer = null;
        System.out.print("Would you like lemon with your tea (y/n)? ");
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        try {
            answer = in.readLine();
        } catch (IOException ioe) {
            System.err.println("IO error trying to read your answer");
        }
        if (answer == null) {
            return "no";
        }
        return answer;
    }
}

测试代码

// BeverageTestDrive.java
public class BeverageTestDrive {
    public static void main(String[] args) {
                             
        Tea tea = new Tea();
        Coffee coffee = new Coffee();
                             
        System.out.println("\nMaking tea...");
        tea.prepareRecipe();
                             
        System.out.println("\nMaking coffee...");
        coffee.prepareRecipe();
                             
        TeaWithHook teaHook = new TeaWithHook();
        CoffeeWithHook coffeeHook = new CoffeeWithHook();
                             
        System.out.println("\nMaking tea...");
        teaHook.prepareRecipe();
                             
        System.out.println("\nMaking coffee...");
        coffeeHook.prepareRecipe();
    }
}

运行效果