Strategy Design pattern - Implementation [Compress files]

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Real-World Scenario: File Compression

When developing applications that store or transfer large volumes of files, compressing files is a critical requirement. Different formats serve different needs:

• Zip Compression: Universally supported and fast across almost all platforms.
• Rar Compression: Delivers high compression ratios for archiving large assets.
• 7z / Tar.gz: Popular choices in modern developer environments and Unix systems.

Hardcoding these compression techniques inside a file archiver class makes your application rigid and violates object-oriented design principles. The Strategy Design Pattern solves this problem by encapsulating each compression technique into an independent, interchangeable class.

Key Components of the Architecture

• CompressionStrategy (Interface): Declares a contract method such as compress(List<File> files) shared across all algorithms.
• Concrete Strategy Classes: Specific implementations like ZipCompressionStrategy and RarCompressionStrategy containing format-specific algorithms.
• CompressionContext (Context): Maintains a reference to the active compression strategy and triggers the compression workflow without needing to know implementation details.

Java Code Walkthrough

1. Define the Common Strategy Interface:

import java.io.File;
import java.util.List;

public interface CompressionStrategy {
    void compressFiles(List<File> files);
}

2. Implement Concrete Strategies:

public class ZipCompressionStrategy implements CompressionStrategy {
    @Override
    public void compressFiles(List<File> files) {
        System.out.println("Compressing files using ZIP compression format...");
    }
}

public class RarCompressionStrategy implements CompressionStrategy {
    @Override
    public void compressFiles(List<File> files) {
        System.out.println("Compressing files using RAR compression format...");
    }
}

3. Configure the Context Class:

public class CompressionContext {
    private CompressionStrategy compressionStrategy;

    public void setCompressionStrategy(CompressionStrategy compressionStrategy) {
        this.compressionStrategy = compressionStrategy;
    }

    public void createArchive(List<File> files) {
        compressionStrategy.compressFiles(files);
    }
}

Why This Design Pattern Works Best

• Open/Closed Principle (OCP): Need to introduce 7-Zip or GZip? Just create a new class implementing CompressionStrategy without modifying existing code.
• Clean and Readable: Completely eliminates massive conditional if-else or switch-case statements.
• Dynamic Selection: Your application can choose the ideal compression format at runtime based on user preference or file type.

Related Design Pattern Tutorials to Watch Next

• Strategy Design Pattern Explained: Real-Time File Compression Scenario
• Strategy Design Pattern: Class Diagram Explained
• Strategy Design Pattern: Sequence Diagram Walkthrough

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Strategy Design pattern - Implementation [Compress files]

Strategy Design pattern - Implementation [Compress files] - Class Diagram

CompressionStrategy.java

import java.io.File;

import java.util.ArrayList;

public interface CompressionStrategy

{

public void compressFiles( ArrayList<File> files,String compressedArchiveFileName );

}

ZipCompressionStrategy.java

import java.io.File;

import java.util.ArrayList;

public class ZipCompressionStrategy implements CompressionStrategy

{

public void compressFiles( ArrayList<File> files, String compressedArchiveFileName )

{

System.out.println("Files are compressed using zip approach: '" + compressedArchiveFileName

               + ".zip' file is created");

}

}

RarCompressionStrategy.java

import java.io.File;

import java.util.ArrayList;

public class RarCompressionStrategy implements CompressionStrategy

{

public void compressFiles( ArrayList<File> files, String compressedArchiveFileName )

{

System.out.println("Files are compressed using Rar approach: '" + compressedArchiveFileName

               + ".rar' file is created");

}

}

CompressionContext.java

import java.io.File;

import java.util.ArrayList;

public class CompressionContext

{

private CompressionStrategy strategy;

//Client will set what CompressionStrategy to use by calling this method

public void setCompressionStrategy( CompressionStrategy strategy )

{

this.strategy = strategy;

}

public void createArchive( ArrayList<File> files,String compressedArchiveFileName )

{

strategy.compressFiles(files,compressedArchiveFileName);

}

}

Client.java

import java.io.File;

import java.util.ArrayList;

public class Client

{

public static void main( String[] args )

{

ArrayList<File> fileList = new ArrayList<File>();

fileList.add(new File("D:\\Javafiles\\Javadoc.txt"));

fileList.add(new File("D:\\Javafiles\\Release.txt"));

CompressionContext ctx = null;

ctx = new CompressionContext();

ctx.setCompressionStrategy(new ZipCompressionStrategy());

ctx.createArchive(fileList,"Javafiles");

ctx = new CompressionContext();

ctx.setCompressionStrategy(new RarCompressionStrategy());

ctx.createArchive(fileList,"Javafiles");

}

}

Output

Files are compressed using zip approach: 'Javafiles.zip' file is created

Files are compressed using Rar approach: 'Javafiles.rar' file is created

See also:

Strategy Design pattern - Introduction

Strategy Design pattern - Real Time Example [Compress files]

Strategy Design pattern - Real Time Example [Payment]

Strategy Design pattern - Real Time Example [Travel]

Strategy Design pattern - Real Time Example [Sorting]

Strategy Design pattern - Real Time Example [Search]

Strategy Design pattern - Class Diagram

Strategy Design pattern - Sequence Diagram

Strategy Design pattern - Implementation [Travel]

Strategy Design pattern - Implementation [Payment]

Strategy Design pattern - Implementation [Search]

Strategy Design pattern - Implementation [Sort]

Strategy Design pattern - KeyPoints

All Design Patterns Links