8  Template Method Pattern

Q: What is “template method pattern” in software design? Explain and give simple example in Dart.

The Template Method Pattern is a behavioral design pattern that defines the skeleton of an algorithm in a base class, letting subclasses override specific steps without changing the algorithm’s structure.

8.1 Core Concept

The pattern uses a “template method” that calls several abstract or virtual methods in a specific order. Subclasses implement these methods to customize behavior while maintaining the overall flow.

Base Class
    │
    ├── template_method() ← Fixed algorithm structure
    │   ├── step1()
    │   ├── step2() 
    │   └── step3()
    │
    └── Abstract methods that subclasses must implement

8.2 Simple Dart Example

Let’s create a data processing template:## Key Benefits

Structure Consistency: All processors follow the same 4-step workflow (load → validate → transform → save)

Code Reuse: The template method in the base class eliminates duplication

Extensibility: Easy to add new data formats (XML, Excel) by extending the base class

Maintainability: Algorithm changes happen in one place

8.3 When to Use

• Multiple classes have similar algorithms with slight variations
• You want to control the algorithm structure while allowing customization
• Common in frameworks (like Flutter’s widget lifecycle methods)

The pattern is particularly useful in radiology data processing where you might handle DICOM, NIfTI, or other medical imaging formats using the same processing pipeline but different implementation details.