Template method design pattern

What is the template method design pattern?

The template method design pattern defines the skeleton of an algorithm in the superclass but lets subclasses override the algorithm without changing its structure. It is a behavioral design pattern

Advantages of template method design pattern:

We can let clients override only certain parts of a large algorithm, making them less affected by changes that happen to other parts of the algorithm.
We can pull the duplicate code into a superclass.
Code reuse happens with the Template Method pattern as it uses inheritance and not composition
Flexibility lets subclasses decide how to implement steps in an algorithm

Disadvantages of template method design pattern:

Template methods tend to be harder to maintain the more steps they have
We might violate the Liskov Substitution Principle by suppressing a default step implementation via a subclass
Debugging and understanding the sequence of flow in the Template Method pattern can be confusing

Difference between Template method and Strategy design pattern

Template Method	Strategy
The abstract class defines the invariant behaviors, while the implementing classes defined the dependent methods	In a strategy, the behavior implementations are independent — each implementing class defines the behavior and there is no code shared between them
Template method may define a set of public methods as well as a set of supporting private primitives that subclasses must implement	Strategies have a single public method — the execute() method
It’s based on inheritance	It’s based on delegation/composition
Parent class completely controls the algorithm and differs only in certain steps from concrete classes	It changes the behavior of the object at run time by completely replacing one algorithm with another algorithm at run time
Binding is done at compile time	Binding is done at run time

Example of template method design pattern:

// client.ts
import PdfMiner from './subclass/PdfMiner'
import JsonMiner from './subclass/JsonMiner'


const dataMiner = new PdfMiner();
dataMiner.templateMethod();


console.log("==========================================");

const jsonMiner = new JsonMiner();
jsonMiner.templateMethod();

Output:
PdfMiner says: I have implemented openFile
PdfMiner says: I have implemented extractData
PdfMiner says: I have implemented processData
AbstractClass says: I am doing the data analysis work 
AbstractClass says: I will send the report after analyzing the data
PdfMiner says: I have implemented closeFile
==========================================
JsonMiner says: I have implemented openFile
JsonMiner says: I have implemented extractData
JsonMiner says: I have implemented processData
AbstractClass says: I am doing the data analysis work 
AbstractClass says: I will send the report after analyzing the data
JsonMiner says: I have implemented closeFile


// DataMiner.ts
export default abstract class DataMiner {
    /**
     * The template method defines the skeleton of an algorithm.
     */
    public templateMethod(): void {
        this.openFile();
        this.extractData();
        this.processData();
        this.analyzeData();
        this.sendReport();
        this.closeFile();
    }

    /**
     * These operations already have implementations.
     */
    protected analyzeData(): void {
        console.log('AbstractClass says: I am doing the data analysis work ');
    }

    protected sendReport(): void {
        console.log('AbstractClass says: I will send the report after analyzing the data');
    }

    /**
     * These operations have to be implemented in subclasses.
     */
    protected abstract openFile(): void;
    protected abstract extractData(): void;
    protected abstract processData(): void;
    protected abstract closeFile(): void;
}


// PdfMiner.ts
import DataMiner from '../DataMiner'

export default class PdfMiner extends DataMiner {

    protected openFile(): void {
        console.log('PdfMiner says: I have implemented openFile');
    }

    protected extractData(): void {
        console.log('PdfMiner says: I have implemented extractData');
    }

    protected processData(): void {
        console.log('PdfMiner says: I have implemented processData');
    }

    protected closeFile(): void {
        console.log('PdfMiner says: I have implemented closeFile');
    }

}




// JsonMiner.ts
import DataMiner from '../DataMiner'

export default class JsonMiner extends DataMiner {

    protected openFile(): void {
        console.log('JsonMiner says: I have implemented openFile');
    }

    protected extractData(): void {
        console.log('JsonMiner says: I have implemented extractData');
    }

    protected processData(): void {
        console.log('JsonMiner says: I have implemented processData');
    }

    protected closeFile(): void {
        console.log('JsonMiner says: I have implemented closeFile');
    }

}

Source code: Template method design pattern github link

Reference

What is the template method design pattern?

Advantages of template method design pattern:

Disadvantages of template method design pattern:

Difference between Template method and Strategy design pattern

Example of template method design pattern:

Output:

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