Template Method Design Pattern in Kotlin

1. Definition

The Template Method Design Pattern defines the structure of an algorithm in a method, deferring some steps to subclasses. It allows subclasses to redefine certain steps of an algorithm without changing its structure.

2. Problem Statement

Imagine designing a data mining application that extracts, analyzes, and generates a report for different data formats. While the steps for mining are consistent (extract, analyze, report), the specifics can differ based on the data format, like CSV or XML.

3. Solution

The Template Method suggests moving the invariant parts of the algorithm to a base class, while specific steps are either abstract or have a default implementation. Subclasses can provide concrete behavior without changing the algorithm's structure.

4. Real-World Use Cases

1. Preparing a beverage where the preparation steps are the same, but ingredients or process might differ, e.g., coffee vs. tea.

2. Data parsers for different formats, e.g., XML and CSV, where the parsing algorithm is consistent, but specific steps may vary.

5. Implementation Steps

1. Create an abstract class with the template method.

2. Within this class, provide default implementations or abstract definitions for the variable steps.

3. Derive subclasses from the abstract class to implement specific behaviors.

6. Implementation in Kotlin Programming

// Step 1: Abstract Class with Template Method
abstract class DataMiner {
    fun mineData() {
        extractData()
        analyzeData()
        generateReport()
    }
    abstract fun extractData()
    abstract fun analyzeData()
    fun generateReport() {
        println("Generating report based on analysis.")
    }
}
// Step 2: Concrete Implementations
class CSVDataMiner : DataMiner() {
    override fun extractData() {
        println("Extracting data from CSV file.")
    }
    override fun analyzeData() {
        println("Analyzing CSV data.")
    }
}
class XMLDataMiner : DataMiner() {
    override fun extractData() {
        println("Extracting data from XML file.")
    }
    override fun analyzeData() {
        println("Analyzing XML data.")
    }
}
// Client Code
fun main() {
    val csvMiner = CSVDataMiner()
    csvMiner.mineData()
    val xmlMiner = XMLDataMiner()
    xmlMiner.mineData()
}

Output:

Extracting data from CSV file.
Analyzing CSV data.
Generating report based on analysis.
Extracting data from XML file.
Analyzing XML data.
Generating report based on analysis.

Explanation:

1. DataMiner is the abstract class containing the template method mineData, which outlines the algorithm's structure.

2. Specific steps, like extractData and analyzeData, are abstract and must be implemented by subclasses.

3. generateReport has a default implementation which can be overridden by subclasses if needed.

4. Concrete classes, CSVDataMiner and XMLDataMiner, provide specific implementations for extracting and analyzing data.

5. The client code demonstrates the algorithm's consistency, with specifics handled by respective subclasses.

7. When to use?

Use the Template Method pattern when:

1. You want to let clients extend only particular steps of a large algorithm.

2. Common behavior among subclasses should be factored out to avoid code duplication.

3. You need to control extensions by subclasses in the algorithm.