JAVA设计模式---模板方法

1、定义： 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，模板方法使得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。

（为了防止子类改变模板方法中的算法，可以将模板方法声明为final）

2、钩子（hook）是一种方法，它在抽象类中不做事，或者只做默认的事情，子类可以选择要不要去覆盖它。

3、实例：

1）需求：
　　冲咖啡步骤： 把水煮沸--->用沸水冲泡咖啡--->把咖啡倒进杯子里--->加糖和牛奶
　　冲茶步骤： 把水煮沸--->用沸水冲泡茶--->把茶倒进杯子里--->加柠檬片
　使用模板方法抽取公共类并实现具体动作，子类通过hook覆盖父类中需要的方法。

2）代码实现：

　　a）抽象父类

public abstract class CaffeineBeverageWithHook {
    public void prepareRecip(){
        boliWater();
        brew();
        pourInCup();
        if(customerWantCondiments()){
            addCondiments();
        }
    }

    abstract void brew();

    abstract void addCondiments();

    public void boliWater(){
        System.out.println("Bolling water");
    }

    public void pourInCup() {
        System.out.println("Pouring into Cup");
    }

    boolean customerWantCondiments(){
        return true;
    }
}

　　b) 子类具体实现

public class CoffeeWithHook extends CaffeineBeverageWithHook {

    @Override
    void brew() {
        System.out.println("Dripping Coffee through filter");
    }

    @Override
    void addCondiments() {
        System.out.println("Adding Suger and Milk");
    }

    public boolean customerWantCondiments() {
        String answer = getUserInput();
        if (answer.toLowerCase().startsWith("y")) {
            return true;
        } else {
            return false;
        }
    }

    private String getUserInput() {
        String answer = "no";
        System.out.println("Would you like some suger and milk (y/n)?: ");
        BufferedReader in = new BufferedReader(new InputStreamReader((System.in)));
        try {
            answer = in.readLine();
        } catch (IOException e) {
            System.out.println("IO error!");
        }
        return answer;
    }
}

public class TeaWithHook extends CaffeineBeverageWithHook{

    @Override
    void brew() {
        System.out.println("Dripping tea through filter");
    }

    @Override
    void addCondiments() {
        System.out.println("Adding lemon");
    }

    public boolean customerWantCondiments() {
        String answer = getUserInput();
        if (answer.toLowerCase().startsWith("y")) {
            return true;
        } else {
            return false;
        }
    }

    private String getUserInput() {
        String answer = "no";
        System.out.println("Would you like some lemon (y/n)?: ");
        BufferedReader in = new BufferedReader(new InputStreamReader((System.in)));
        try {
            answer = in.readLine();
        } catch (IOException e) {
            System.out.println("IO error!");
        }
        return answer;
    }
}

　　c）测试类

public class CaffineBeverageTest {
    public static void main(String[] args) {
        TeaWithHook teaHook = new TeaWithHook();
        CoffeeWithHook coffeeHook = new CoffeeWithHook();

        System.out.println("\n============Making Tea start===========");
        teaHook.prepareRecip();
        System.out.println("\n=============Making Tea end============");

        System.out.println("\n============Making Coffee start===========");
        coffeeHook.prepareRecip();
        System.out.println("\n=============Making Coffee end============");
    }
}

　　测试结果：

============Making Tea start===========
Bolling water
Dripping tea through filter
Pouring into Cup
Would you like some lemon (y/n)?:
n

=============Making Tea end============

============Making Coffee start===========
Bolling water
Dripping Coffee through filter
Pouring into Cup
Would you like some suger and milk (y/n)?:
y
Adding Suger and Milk

=============Making Coffee end============