Template Method Pattern

The Template Method Pattern helps when you have a process that mostly follows the same steps, but some parts need to change depending on the situation.

You define the overall structure of the process in a base class, and the variable steps can be customized in subclasses.

Think of it like a cooking recipe: the main steps are the same for everyone, but each cook can add their own twist to some steps without changing the overall recipe.

This makes your code reusable, consistent, and easier to maintain.

Components of the Template Method Pattern

• 1. Abstract Class/Interface: Holds the template method (the main workflow) and defines steps, some with default logic and some left for subclasses.

  2. Template Method: The main method that calls steps in order, often marked final to protect the workflow.

  3. Abstract/Hook Methods: Steps that subclasses must implement or can optionally override.

  4. Concrete Subclasses: Subclasses that fill in the specific steps while keeping the main workflow intact.

  How to Implement

  1. Create an Abstract Class: Define the overall algorithm structure.

  2. Define the Template Method: Add a method that runs each step in order.

  3. Implement Core Steps: Some steps can have default logic, others stay abstract for customization.

  4. Create Subclasses: Subclasses override the necessary steps without changing the workflow.

  5. Use the Template Method: Run the template method on a subclass instance. It will execute all steps in the right order with custom behavior where needed.

   

When to Use It?

Use this pattern when:

• You have a process that mostly stays the same, but some steps need to change depending on the situation.

• You want to avoid repeating code in similar workflows.

• You want to give flexibility to subclasses to customize certain steps while keeping the main structure fixed.

  When not to use it ?

  • The steps of the process are very different each time, so the shared structure isn’t useful.

  • The steps are tightly connected, so changing one step affects the others.

  • You need to frequently change the process at runtime, because the template is designed to keep the structure fixed.

  This keeps your code organized, reusable, and easy to maintain without unnecessary repetition.

  Example: Baking a Cake

Baking a cake always follows the same basic steps:

1. Preheat the oven

2. Mix the ingredients

3. Bake

What changes is the flavor—chocolate, vanilla, or another type. The main steps stay the same, only the details vary. This is exactly how the Template Method works: the overall structure is fixed, but subclasses can customize specific steps.

Use Case: ML Model Pipelines

Training a machine learning model usually involves:

1. Loading the data

2. Building the model

3. Evaluating results

Different models like neural networks, decision trees, or SVMs , have unique building steps, but the overall workflow stays the same. The Template Method lets you define the common pipeline once and allow each model to handle its own specific steps.

This approach saves time, avoids repeating code, and keeps your workflows organized.

UML Design

 

Benefits of the Template Method Pattern

• Code Reusability: Common logic is kept in the base class, so you don’t repeat it in every subclass.

• Customizability: Subclasses can implement their own specific steps.

• Controlled Workflow: Important steps are fixed and cannot be skipped.

• Cleaner Code: Reduces repeated code across similar processes.

Best Practices

• Mark the template method as final so its overall order cannot be changed.

• Use abstract methods for steps that every subclass must implement.

• Provide hook methods for optional steps that subclasses can override if needed.

 

Summary

The Template Method Pattern sets a fixed workflow but allows subclasses to change certain steps. It’s like a cake recipe: the main steps preheat, mix, bake stay the same, but each cook can choose a different flavor. This makes your code easier to reuse, maintain, and keep consistent. It is helpful when you have similar processes that need small changes, like machine learning pipelines, UI rendering, or testing frameworks.

Code

By Coder Army