Template Method Design Pattern

Last updated on Jan 22, 2023

I. Introduction

A. Explanation of the Method Template Design Pattern

The Template Method Design Pattern is a behavioral design pattern that defines the skeleton of an algorithm in a method, called the template method, and allows subclasses to redefine certain steps of the algorithm without changing its overall structure.

The key idea behind the template method is to provide a common structure for similar algorithms, while allowing subclasses to provide their own implementation for certain steps. This allows for code reuse and eliminates the need for code duplication.

The template method typically consists of a series of steps that are performed in a specific order. These steps are often implemented as abstract methods, which are then overridden by subclasses to provide their own implementation. The template method then calls these overridden methods in the correct order to execute the algorithm.

One example of the template method pattern is the creation of a game. The template method would define the overall structure of the game, such as the initialization, the game loop, and the cleanup. Subclasses would then provide their own implementation for the game loop, such as a first-person shooter or a platformer.

B. Use cases for the Method Template Design Pattern

The Template Method Design Pattern is a widely used pattern in software development, and has many different use cases. Some of the most common use cases include:

Creating frameworks: The template method pattern is often used to create frameworks, such as game engines or web frameworks. These frameworks provide a common structure for developers to follow, while allowing them to customize certain aspects of the framework to suit their needs.
Simplifying complex algorithms: The template method pattern can be used to simplify complex algorithms by breaking them down into smaller, more manageable steps. This makes the algorithm easier to understand, test, and maintain.
Enforcing a specific order of operations: The template method pattern can be used to enforce a specific order of operations, such as a series of steps that must be performed in a specific order. This can be useful for ensuring that certain preconditions are met before certain operations are performed.
Creating pluggable systems: The template method pattern can be used to create pluggable systems, where developers can add new functionality to an existing system by providing their own implementation of certain steps. This can be useful for creating extensible systems that can adapt to changing requirements.
Creating reusable code: The template method pattern can be used to create reusable code, by providing a common structure for similar algorithms and allowing developers to provide their own implementation for certain steps. This can help to reduce code duplication and improve maintainability.

C. Comparison to other design patterns

The Template Method Design Pattern is a behavioral design pattern, which means it deals with the communication between objects and how they operate. It is similar to other behavioral design patterns such as the Strategy Pattern, the State Pattern, and the Observer Pattern.

The Strategy Pattern is also a behavioral pattern that defines a family of algorithms, encapsulating each one and making them interchangeable. However, the key difference between the two patterns is that the strategy pattern provides a way to switch the algorithm at runtime, whereas the template method pattern defines the skeleton of the algorithm and allows subclasses to provide their own implementation for certain steps.

The State Pattern is also a behavioral pattern that allows an object to alter its behavior when its internal state changes. The State pattern is used to change the behavior of an object based on its internal state, whereas the template method pattern is used to provide a common structure for similar algorithms and allows subclasses to provide their own implementation for certain steps.

The Observer Pattern is a behavioral pattern that allows objects to be notified of changes to other objects. The observer pattern is used to notify objects of changes to other objects, whereas the template method pattern is used to provide a common structure for similar algorithms and allows subclasses to provide their own implementation for certain steps.

In summary, the Template Method Design Pattern is similar to other behavioral design patterns, such as the Strategy Pattern, the State Pattern, and the Observer Pattern. The main difference between these patterns is the intent and the way they are used. The template method pattern is used to provide a common structure for similar algorithms and allows subclasses to provide their own implementation for certain steps, the strategy pattern provides a way to switch the algorithm at runtime, the State pattern is used to change the behavior of an object based on its internal state, and the Observer pattern is used to notify objects of changes to other objects.

II. Understanding the Method Template Design Pattern

A. Definition and explanation of the key elements

The key elements of the Template Method Design Pattern are:

The Abstract Class: This class defines the template method and the common structure of the algorithm. It also defines abstract methods that will be overridden by subclasses to provide their own implementation for certain steps of the algorithm.
The Concrete Classes: These classes inherit from the abstract class and provide their own implementation for the abstract methods defined in the abstract class. They can also add additional functionality to the algorithm.
The Template Method: This is the method defined in the abstract class that provides the overall structure of the algorithm. It calls the abstract methods in a specific order to execute the algorithm.
The Hook Method: This is an optional method that can be defined in the abstract class. It is called by the template method and can be overridden by subclasses to provide additional functionality to the algorithm.
The Client: The client is the code that uses the template method pattern to create objects. The client calls the template method on the created object to execute the algorithm.

C. Code example of a basic implementation

Here's an example of a basic implementation of the Template Method Design Pattern in Java:

// Abstract class that defines the template method and abstract methods
abstract class Game {
    // Template method
    public final void play() {
        initialize();
        startPlay();
        endPlay();
    }

    // Abstract methods to be overridden by subclasses
    public abstract void initialize();
    public abstract void startPlay();
    public abstract void endPlay();
}

// Concrete class that inherits from the abstract class
class Cricket extends Game {
    @Override
    public void initialize() {
        System.out.println("Cricket Game Initialized! Start playing.");
    }

    @Override
    public void startPlay() {
        System.out.println("Cricket Game Started. Enjoy the game!");
    }

    @Override
    public void endPlay() {
        System.out.println("Cricket Game Finished!");
    }
}

// Concrete class that inherits from the abstract class
class Football extends Game {
    @Override
    public void initialize() {
        System.out.println("Football Game Initialized! Start playing.");
    }

    @Override
    public void startPlay() {
        System.out.println("Football Game Started. Enjoy the game!");
    }

    @Override
    public void endPlay() {
        System.out.println("Football Game Finished!");
    }
}

// Client code
public class Main {
    public static void main(String[] args) {
        Game game = new Cricket();
        game.play();

        game = new Football();
        game.play();
    }
}

In this example, the abstract class Game defines the template method play() which calls the abstract methods initialize(), startPlay() and endPlay() in a specific order to execute the algorithm. The concrete classes Cricket and Football inherit from the Game class and provide their own implementation for the abstract methods. The client code creates objects of the concrete classes and calls the template method to execute the algorithm.

This example shows a basic implementation of the Template Method Design Pattern in Java, where the template method defines the skeleton of the algorithm, and concrete classes provide their own implementation for certain steps of the algorithm. This pattern allows to reuse the common structure of the algorithm and adapt it to different situations.

III. Advantages and Disadvantages

A. Benefits of using the Method Template Design Pattern

The Template Method Design Pattern is a widely used pattern in software development that provides many benefits, including:

Code reuse: The template method pattern allows for code reuse by providing a common structure for similar algorithms and allowing developers to provide their own implementation for certain steps. This can help to reduce code duplication and improve maintainability.
Flexibility: The template method pattern provides flexibility by allowing subclasses to provide their own implementation for certain steps of the algorithm. This can be useful for creating extensible systems that can adapt to changing requirements.
Simplifies complex algorithms: The template method pattern can be used to simplify complex algorithms by breaking them down into smaller, more manageable steps. This makes the algorithm easier to understand, test, and maintain.
Enforces a specific order of operations: The template method pattern can be used to enforce a specific order of operations, such as a series of steps that must be performed in a specific order. This can be useful for ensuring that certain preconditions are met before certain operations are performed.
Reusability across different contexts: The template method pattern can be used to create reusable code that can be used across different contexts, such as different projects, different teams, and different industries.
Easy testing: The template method pattern allows for easy testing by breaking down the algorithm into smaller, more manageable steps, making it easier to test each step individually.

In summary, the Template Method Design Pattern is a widely used pattern in software development that provides many benefits, including code reuse, flexibility, simplification of complex algorithms, enforcement of specific order of operations, reusability across different contexts and easy testing. It is a powerful tool for creating flexible and reusable code, and it is widely used in many different industries.

B. Drawbacks to consider when using the pattern

While the Template Method Design Pattern is a powerful tool for creating flexible and reusable code, there are some drawbacks to consider when using the pattern:

Increased complexity: The template method pattern can increase the complexity of the codebase by adding an additional level of abstraction. Developers need to understand the template method and the abstract methods it calls, as well as the concrete classes that provide the implementation for those methods.
Limited flexibility: The template method pattern can be limiting in terms of flexibility as it defines the overall structure of the algorithm and the order in which the steps are executed. Subclasses are allowed to provide their own implementation for certain steps, but they cannot change the overall structure of the algorithm.
Overuse can lead to code bloat: If the template method pattern is overused, it can lead to code bloat and make the codebase harder to understand and maintain. It's important to use the pattern only when it is truly necessary, and not to use it as a catch-all solution for every problem.
Hard to change the existing structure: If the existing structure is hardcoded it can be difficult to change it, in such case developers have to override the whole template method to change the structure of the algorithm.
Hard to add new functionality: Adding new functionality to the algorithm can be difficult, as it may require changes to the template method and the abstract methods it calls.

While the Template Method Design Pattern is a powerful tool for creating flexible and reusable code, it's important to be aware of its drawbacks. The pattern can increase the complexity of the codebase, be limiting in terms of flexibility, lead to code bloat, hard to change the existing structure, and hard to add new functionality. Developers should carefully evaluate the pros and cons of using the pattern before implementing it in their codebase.

V. Conclusion

A. Additional resources for learning more about the Method Template Design Pattern

There are many resources available for learning more about the Template Method Design Pattern, including:

Books: "Design Patterns: Elements of Reusable Object-Oriented Software" by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides is a classic book that provides a comprehensive introduction to the Template Method Design Pattern and other design patterns.
Online tutorials and articles: There are many online tutorials and articles available that provide detailed explanations and examples of the Template Method Design Pattern. Some popular websites for learning about design patterns include SourceMaking, Refactoring.Guru, and Pluralsight.
YouTube videos: There are many YouTube videos available that provide an overview and examples of the Template Method Design Pattern. You can find a variety of videos from different sources, including tutorials, lectures, and screencasts.
Online courses: There are many online courses available that cover the Template Method Design Pattern and other design patterns. Some popular platforms for learning about design patterns include Udemy, Coursera, and LinkedIn Learning.
Open-source code: There are many open-source projects available that use the Template Method Design Pattern. Reviewing the source code of these projects can be a great way to learn about the pattern and see it in action.