Mastering Design Patterns: Introduction
An Introduction to Design Patterns
Are you dreaming of coding super sturdy, easy-to-maintain, and slick code that won't become obsolete next year? Well, it's not just a dream! It can be your reality, thanks to something called Design Patterns. But you might be asking yourself, "What on earth are Design Patterns, and why do they matter?" Don't worry, we've got you covered. In this article, we will help to clear up any confusion about this key player in the coding world. We'll be chatting about what Design Patterns are, why they're pretty important, and we'll throw in some cool examples from the popular book, "Head First Design Patterns" by Eric Freeman, Ph.D. , Elisabeth Robson , Bert Bates, and Kathy Sierra. So, let's dive in and discover the magic of Design Patterns together!
What are Design Patterns?
Design Patterns are reusable solutions to common problems that occur in software design. They are best practices, established over time, and provide templates designed to help solve recurring design problems, thus making our code more flexible, reusable, and maintainable. Design Patterns aren't complete designs that can be transformed directly into source or machine code. Instead, they are descriptions or templates for how to solve a problem that can be applied in many different situations.
The Gang of Four (GoF), a group of four authors, first brought Design Patterns to the limelight with their seminal book "Design Patterns: Elements of Reusable Object-Oriented Software". For beginners, though, "Head First Design Patterns" provides a more accessible introduction. This book categorizes design patterns into three groups:
Why are Design Patterns Used?
Design Patterns are vital in software development for several reasons:
Design Patterns taken from "Head First Design Patterns"
The Design Patterns we are going to talk about aren't the only ones out there. The list is much longer! However, the ones that are listed below, are most commonly used.
Design Principles
"Head First Design Patterns" highlights several important design principles throughout the book. These principles serve as a foundation for the design patterns and their use in effective software development.
Examples: Strategy Design Pattern
The Strategy pattern is a behavioural design pattern that enables an algorithm's behavior to be selected at runtime. In Java, the Strategy pattern can be implemented using dependency injection, which allows you to inject different strategy classes to change the behavior of the application. Here is a simple example:
Let's assume we're developing an application that can process different types of files (XML, JSON, CSV). We can create a strategy for each file type:
Define the IFileStrategy interface. We added "I" prefix to specify that's an interface
package com.kubrik.designPatterns.strategy
public interface IFileStrategy {
void processFile(String fileName);
};
2. Json File Strategy
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package com.kubrik.designPatterns.strategy
public class JsonFileStrategy implements IFileStrategy {
@Override
public void processFile(String fileName) {
// JSON processing
System.out.println("Processing JSON file " + fileName);
}
};
3. Csv File Strategy
package com.kubrik.designPatterns.strategy
public class CsvFileStrategy implements IFileStrategy {
@Override
public void processFile(String fileName) {
// CSV processing
System.out.println("Processing CSV file " + fileName);
}
};
4. XML File Strategy
package com.kubrik.designPatterns.strategy
public class XMLFileStrategy implements IFileStrategy {
@Override
public void processFile(String fileName) {
// XML processing
System.out.println("Processing XML file " + fileName);
}
}
;
5. File Processor
At this point, we need someone who would be interacting with the files and picking up at run time the appropriate strategy. Let's create our File Processor service.
package com.kubrik.designPatterns.strategy
import java.util.Map;
import java.util.Objects;
public class FileProcessor {
private final Map<String, IFileStrategy> fileStrategyMap;
public FileProcessor(Map<String, IFileStrategy> fileStrategyMap) {
this.fileStrategyMap = fileStrategyMap;
}
public void processFile(String fileType, String fileName) {
IFileStrategy fileStrategy = fileStrategyMap.get(fileType);
if (Objects.nonNull(fileStrategy)) {
fileStrategy.processFile(fileName);
} else {
throw new IllegalArgumentException("Invalid file type: " + fileType);
}
}
}
In all scenarios, when working within a Spring Boot application, you can utilize the @Service and @Autowired annotations to streamline the creation of instances. These annotations enable Spring's powerful Dependency Injection mechanism, thus saving you from manually orchestrating object creation and association.
6. Testing The Application
Finally, let's test our application.
package com.kubrik.designPatterns.strategy
import java.util.Map;
public class Main {
public static void main(String[] args) {
// write your code here
JsonFileStrategy jsonFileStrategy = new JsonFileStrategy();
XMLFileStrategy xmlFileStrategy = new XMLFileStrategy();
CsvFileStrategy csvFileStrategy = new CsvFileStrategy();
FileProcessor fileProcessor = new FileProcessor(Map.of("json", jsonFileStrategy,"xml",xmlFileStrategy,
"csv",csvFileStrategy));
fileProcessor.processFile("json", "MyJsonFile.json");
fileProcessor.processFile("csv", "MyCSVFile.csv");
fileProcessor.processFile("xml", "MyXMLFile.xml");
}
};
The output:
Processing JSON file MyJsonFile.json
Processing CSV file MyCSVFile.csv
Processing XML file MyXMLFile.xml
Process finished with exit code 0n
Explanation:
In our example, we've architected an IFileStrategy interface and have subsequently brought to life three distinct strategies for the processing of JSON, XML, and CSV files. Leveraging Spring's dependency injection, we can then weave these strategies into the very fabric of a FileProcessor service.?This is where the true potency of the Strategy pattern is revealed. The FileProcessor service, acting as a conductor, uses the appropriate strategy at runtime to process different types of files. Yet, it remains blissfully unaware of the internal workings of these file strategies, unburdened by the specifics of how they fulfil their tasks.?Its focus is solely on their common interface, processFile, which guarantees a standard method for file processing regardless of the file type. By focusing on this interface, the FileProcessor service can fluidly coordinate the processing of various file types without getting entangled in the intricate details of each specific processing strategy. This epitomizes the key principle of the Strategy pattern – encapsulating the what (the task) from the how (the implementation).
Code repository
Conclusion
Design Patterns, as we've seen, are powerful tools that software developers can use to solve common problems. Understanding these patterns can make one's code more efficient, readable, and maintainable. However, it's essential to remember that while they're beneficial, they are not a cure-all solution and should not be used indiscriminately. They should be viewed as guiding principles, not rigid rules, and used when and where appropriate.
Throughout this introduction, we've referenced the excellent "Head First Design Patterns". The book provides an engaging, interactive, and visually enriched approach to learning about Design Patterns. Whether you're a junior developer or an experienced engineer, this resource offers a wealth of knowledge that can bolster your software development expertise.
We've covered a broad overview of design patterns in this guide. But remember, the journey doesn't end here. In the next edition of #InsideEngineering, we'll dive deeper into each of these patterns, illuminating their intricacies, providing more detailed examples, and discussing the appropriate scenarios for their application. We believe that understanding these patterns in detail can be a game-changer for your coding skills.?
So stay tuned, keep exploring, and continue your journey into the fascinating world of Design Patterns with us!
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1 年valuable and insightful
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1 年Very insightful!