模板模式

Intent

• Define the skeleton of an algorithm in an operation, deferring some steps to client subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.
• Base class declares algorithm 'placeholders', and derived classes implement the placeholders.

Structure

template by keith

2. 代码:

public class Template {
    abstract class Beverage {
        // template method, make it final so that it can not be redefined
        final void prepareRecipe() {
            boilWater();
            brew();
            pourInCup();
            if (wantCondiments())
                addCondiments();
        }

        abstract void brew();

        abstract void addCondiments();

        void boilWater() {
            System.out.println("Boiling water");
        }

        void pourInCup() {
            System.out.println("Pouring into a cup");
        }

        // hook method, it is up to subclass to decide whether to override it or not
        // the hook method make the algorithm structure more flexible
        boolean wantCondiments() {
            return true;
        }
    }
    class Coffee extends Beverage {

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

        @Override
        void addCondiments() {
            System.out.println("Adding Sugar and Milk");
        }
    }
    class Tea extends Beverage {

        @Override
        void brew() {
            System.out.println("Steeping the tea");
        }

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

        @Override
        boolean wantCondiments() {
            return false;
        }
    }
    private void test() {
        Coffee coffee = new Coffee();
        Tea tea = new Tea();

        coffee.prepareRecipe();
        tea.prepareRecipe();
    }
    public static void main(String[] args) {
        Template template = new Template();
        template.test();
    }
}

3. Output

Boiling water
Dripping Coffee through filter
Pouring into a cup
Adding Sugar and Milk
Boiling water
Steeping the tea
Pouring into a cup

Refenrence

1. Design Patterns
2. 设计模式