Tutorial

Template Method Design Pattern in Java

Published on August 3, 2022
author

Pankaj

Template Method Design Pattern in Java

Template Method is a behavioral design pattern. Template Method design pattern is used to create a method stub and deferring some of the steps of implementation to the subclasses.

Template Method Design Pattern

Template method defines the steps to execute an algorithm and it can provide default implementation that might be common for all or some of the subclasses. Let’s understand this pattern with an example, suppose we want to provide an algorithm to build a house. The steps need to be performed to build a house are - building foundation, building pillars, building walls and windows. The important point is that the we can’t change the order of execution because we can’t build windows before building the foundation. So in this case we can create a template method that will use different methods to build the house. Now building the foundation for a house is same for all type of houses, whether its a wooden house or a glass house. So we can provide base implementation for this, if subclasses want to override this method, they can but mostly it’s common for all the types of houses. To make sure that subclasses don’t override the template method, we should make it final.

Template Method Abstract Class

Since we want some of the methods to be implemented by subclasses, we have to make our base class as abstract class. HouseTemplate.java

package com.journaldev.design.template;

public abstract class HouseTemplate {

	//template method, final so subclasses can't override
	public final void buildHouse(){
		buildFoundation();
		buildPillars();
		buildWalls();
		buildWindows();
		System.out.println("House is built.");
	}

	//default implementation
	private void buildWindows() {
		System.out.println("Building Glass Windows");
	}

	//methods to be implemented by subclasses
	public abstract void buildWalls();
	public abstract void buildPillars();

	private void buildFoundation() {
		System.out.println("Building foundation with cement,iron rods and sand");
	}
}

buildHouse() is the template method and defines the order of execution for performing several steps.

Template Method Concrete Classes

We can have different type of houses, such as Wooden House and Glass House. WoodenHouse.java

package com.journaldev.design.template;

public class WoodenHouse extends HouseTemplate {

	@Override
	public void buildWalls() {
		System.out.println("Building Wooden Walls");
	}

	@Override
	public void buildPillars() {
		System.out.println("Building Pillars with Wood coating");
	}

}

We could have overridden other methods also, but for simplicity I am not doing that. GlassHouse.java

package com.journaldev.design.template;

public class GlassHouse extends HouseTemplate {

	@Override
	public void buildWalls() {
		System.out.println("Building Glass Walls");
	}

	@Override
	public void buildPillars() {
		System.out.println("Building Pillars with glass coating");
	}

}

Template Method Design Pattern Client

Let’s test our template method pattern example with a test program. HousingClient.java

package com.journaldev.design.template;

public class HousingClient {

	public static void main(String[] args) {
		
		HouseTemplate houseType = new WoodenHouse();
		
		//using template method
		houseType.buildHouse();
		System.out.println("************");
		
		houseType = new GlassHouse();
		
		houseType.buildHouse();
	}

}

Notice that client is invoking the template method of base class and depending of implementation of different steps, it’s using some of the methods from base class and some of them from subclass. Output of the above program is:

Building foundation with cement,iron rods and sand
Building Pillars with Wood coating
Building Wooden Walls
Building Glass Windows
House is built.
************
Building foundation with cement,iron rods and sand
Building Pillars with glass coating
Building Glass Walls
Building Glass Windows
House is built.

Template Method Class Diagram

template method design pattern, template design pattern

Template Method Design Pattern in JDK

  • All non-abstract methods of java.io.InputStream, java.io.OutputStream, java.io.Reader and java.io.Writer.
  • All non-abstract methods of java.util.AbstractList, java.util.AbstractSet and java.util.AbstractMap.

Template Method Design Pattern Important Points

  1. Template method should consists of certain steps whose order is fixed and for some of the methods, implementation differs from base class to subclass. Template method should be final.
  2. Most of the times, subclasses calls methods from super class but in template pattern, superclass template method calls methods from subclasses, this is known as Hollywood Principle - “don’t call us, we’ll call you.”.
  3. Methods in base class with default implementation are referred as Hooks and they are intended to be overridden by subclasses, if you want some of the methods to be not overridden, you can make them final, for example in our case we can make buildFoundation() method final because if we don’t want subclasses to override it.

Thats all for template method design pattern in java, I hope you liked it.

Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.

Learn more about our products

About the authors
Default avatar
Pankaj

author

While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the “report an issue“ button at the bottom of the tutorial.

Still looking for an answer?

Ask a questionSearch for more help

Was this helpful?
 
JournalDev
DigitalOcean Employee
DigitalOcean Employee badge
September 2, 2021

Facade is similar to Factory pattern. Template pattern is similar to Strategy/Composite pattern.

- Nakul

    JournalDev
    DigitalOcean Employee
    DigitalOcean Employee badge
    July 13, 2021

    Using above example we can call houseType.buildwalls and houseType.buildPillar

    - Mohsin

      JournalDev
      DigitalOcean Employee
      DigitalOcean Employee badge
      June 16, 2020

      What if I want to use other class instance(let say DAO call or Service layer call) in default method buildWindows() as we can’t use @Autowire for that instance ?

      - Sharath

        JournalDev
        DigitalOcean Employee
        DigitalOcean Employee badge
        June 9, 2020

        Thank you bro

        - Raheem

          JournalDev
          DigitalOcean Employee
          DigitalOcean Employee badge
          February 28, 2019

          How should i know whether the first step is completed or not?

          - Mahadev

            JournalDev
            DigitalOcean Employee
            DigitalOcean Employee badge
            July 26, 2018

            Excellent thank you

            - Mustafa

              JournalDev
              DigitalOcean Employee
              DigitalOcean Employee badge
              July 9, 2018

              That’s a fantastic explanation.

              - Larsen

                JournalDev
                DigitalOcean Employee
                DigitalOcean Employee badge
                July 30, 2017

                explanation is superb.

                - shobhit khandelwal

                  JournalDev
                  DigitalOcean Employee
                  DigitalOcean Employee badge
                  September 25, 2016

                  really helpful. Thanks a lot. :)

                  - Prosenjit

                    JournalDev
                    DigitalOcean Employee
                    DigitalOcean Employee badge
                    December 16, 2015

                    What if I do it like below…the purpose of template method is lost. HouseTemplate houseType = new WoodenHouse(); houseType .buildWindows(); houseType .buildWalls(); houseType .buildPillars(); How to restrict this.

                    - test

                      Try DigitalOcean for free

                      Click below to sign up and get $200 of credit to try our products over 60 days!

                      Sign up

                      Join the Tech Talk
                      Success! Thank you! Please check your email for further details.

                      Please complete your information!

                      Featured on Community

                      Get our biweekly newsletter

                      Sign up for Infrastructure as a Newsletter.

                      Hollie's Hub for Good

                      Working on improving health and education, reducing inequality, and spurring economic growth? We'd like to help.

                      Become a contributor

                      Get paid to write technical tutorials and select a tech-focused charity to receive a matching donation.

                      Welcome to the developer cloud

                      DigitalOcean makes it simple to launch in the cloud and scale up as you grow — whether you're running one virtual machine or ten thousand.

                      Learn more