design-patterns-template-method.md

Template Method

Intent

Define the skeleton of an algorithm and defer some steps to subclasses.

With Template Method, subclasses can redefine certain steps of an algorithm without changing its structure.

Class Diagram

Implementation

Making coffee and tea follows similar processes, but some steps differ. Reuse the code for the shared steps.

public abstract class CaffeineBeverage {

    final void prepareRecipe() {
        boilWater();
        brew();
        pourInCup();
        addCondiments();
    }

    abstract void brew();

    abstract void addCondiments();

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

    void pourInCup() {
        System.out.println("pourInCup");
    }
}

public class Coffee extends CaffeineBeverage {
    @Override
    void brew() {
        System.out.println("Coffee.brew");
    }

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

public class Tea extends CaffeineBeverage {
    @Override
    void brew() {
        System.out.println("Tea.brew");
    }

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

public class Client {
    public static void main(String[] args) {
        CaffeineBeverage caffeineBeverage = new Coffee();
        caffeineBeverage.prepareRecipe();
        System.out.println("-----------");
        caffeineBeverage = new Tea();
        caffeineBeverage.prepareRecipe();
    }
}

boilWater
Coffee.brew
pourInCup
Coffee.addCondiments
-----------
boilWater
Tea.brew
pourInCup
Tea.addCondiments

JDK

• java.util.Collections#sort()
• java.io.InputStream#skip()
• java.io.InputStream#read()
• java.util.AbstractList#indexOf()