SRP.md

Single-Responsibility Principle

What is SRP?

This principle states that a class/method/interface should only have one responsibility. For example:

public class Book {
    // Properties
    private String name;
    private String author;
    private String text;

    // Constructor

    /*
    * Methods relate to the book properties
     */

    // Replace a word in text
    public String replaceWordInText(String word, String replacementWord){
        return text.replaceAll(word, replacementWord);
    }

    // Check if a word is in text
    public boolean isWordInText(String word){
        return text.contains(word);
    }

    /*
    * Method unrelated to the book, it is just output
     */

    // Print text to console
    public void printTextToConsole(){
        System.out.println(text);
    }

    // Getters and setters
}

The Book class should only handle the book properties, but, it violates the SRP because it has two responsibilities: managing the book properties and printing the text to the console. The printTextToConsole method should be in a different class, for example, in a BookPrinter class:

public class BookPrinter {
    /*
     * Method unrelated to the book, it is just output
     */

    // Print the book text to console
    public void printTextToConsole(Book book){
        System.out.println(book.getText());
    }
}

See the source code here.

Why is SRP important?

The SRP is important because it makes the code more readable, maintainable, and testable. It also helps to avoid the God Object anti-pattern.

Hints:

Try to describe the main responsibility of a class, method, or interface. If you can't describe it in a single sentence, it may have more than one responsibility.

Also, try to write the name of the methods describing their responsibility. For example, if you have the signUpAndLogin() method, it probably violates the SRP principle.