Breaking Free from the Evil Singleton TL;DR: Refactor singletons to reduce coupling Problems Addressed High coupling
Difficult testability
Multi-threading issues Related Code Smells https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-vii-8dk31x0?embedable=true https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-v-evj3zs9?embedable=true https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-v-evj3zs9?embedable=true Steps Identify the singleton
Locate all references to its getInstance() method
Refactor the singleton to a standard class
Inject it as a dependency Sample Code Before public class DatabaseConnection {
    private static DatabaseConnection instance;

    private DatabaseConnection() {}

    public static DatabaseConnection getInstance() {
        if (instance == null) {
            instance = new DatabaseConnection();
        }
        return instance;
    }

    public void connect() { 
    }
}

public class Service {
    public void performTask() {
        DatabaseConnection connection = DatabaseConnection.getInstance();
        connection.connect(); 
    }
} After public class DatabaseConnection {  
    // 1. Identify the singleton 
    public void connect() { 
    }
}

public class Service {
    // 2. Locate all references to its getInstance() method.
    private DatabaseConnection connection;

    // 3. Refactor the singleton to a standard class. 
    public Service(DatabaseConnection connection) {
        // 4. Inject it as a dependency.
        this.connection = connection;
    }

    public void performTask() {
        connection.connect(); 
    }
}

DatabaseConnection connection = new DatabaseConnection();
// You can also mock the connection in your tests

Service service = new Service(connection);
service.performTask(); Type [x]Semi-Automatic Safety This refactoring is safe when you update all references to the singleton and handle its dependencies correctly. Testing each step ensures that no references to the singleton are missed. Why Is the Code Better? Refactoring away from a singleton makes the code more modular, testable, and less prone to issues caused by the global state. Injecting dependencies allows you to easily replace DatabaseConnection with a mock or different implementation in testing and other contexts. Tags Coupling Related Refactorings https://maximilianocontieri.com/refactoring-007-extract-class?embedable=true See also https://hackernoon.com/singleton-pattern-the-root-of-all-evil-e4r3up7?embedable=true https://hackernoon.com/coupling-the-one-and-only-software-designing-problem-9z5a321h?embedable=true Credits Image by PublicDomainPictures from Pixabay This article is part of the Refactoring Series. How to Improve Your Code With Easy Refactorings Breaking Free from the Evil Singleton Breaking Free from the Evil Singleton TL;DR: Refactor singletons to reduce coupling TL;DR: Refactor singletons to reduce coupling Problems Addressed High coupling Difficult testability Multi-threading issues High coupling coupling Difficult testability testability Multi-threading issues Related Code Smells https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-vii-8dk31x0?embedable=true https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-vii-8dk31x0?embedable=true https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-v-evj3zs9?embedable=true https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-v-evj3zs9?embedable=true https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-v-evj3zs9?embedable=true https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-v-evj3zs9?embedable=true Steps Identify the singleton Locate all references to its getInstance() method Refactor the singleton to a standard class Inject it as a dependency Identify the singleton Locate all references to its getInstance() method getInstance() Refactor the singleton to a standard class Inject it as a dependency Sample Code Before public class DatabaseConnection {
    private static DatabaseConnection instance;

    private DatabaseConnection() {}

    public static DatabaseConnection getInstance() {
        if (instance == null) {
            instance = new DatabaseConnection();
        }
        return instance;
    }

    public void connect() { 
    }
}

public class Service {
    public void performTask() {
        DatabaseConnection connection = DatabaseConnection.getInstance();
        connection.connect(); 
    }
} public class DatabaseConnection {
    private static DatabaseConnection instance;

    private DatabaseConnection() {}

    public static DatabaseConnection getInstance() {
        if (instance == null) {
            instance = new DatabaseConnection();
        }
        return instance;
    }

    public void connect() { 
    }
}

public class Service {
    public void performTask() {
        DatabaseConnection connection = DatabaseConnection.getInstance();
        connection.connect(); 
    }
} After public class DatabaseConnection {  
    // 1. Identify the singleton 
    public void connect() { 
    }
}

public class Service {
    // 2. Locate all references to its getInstance() method.
    private DatabaseConnection connection;

    // 3. Refactor the singleton to a standard class. 
    public Service(DatabaseConnection connection) {
        // 4. Inject it as a dependency.
        this.connection = connection;
    }

    public void performTask() {
        connection.connect(); 
    }
}

DatabaseConnection connection = new DatabaseConnection();
// You can also mock the connection in your tests

Service service = new Service(connection);
service.performTask(); public class DatabaseConnection {  
    // 1. Identify the singleton 
    public void connect() { 
    }
}

public class Service {
    // 2. Locate all references to its getInstance() method.
    private DatabaseConnection connection;

    // 3. Refactor the singleton to a standard class. 
    public Service(DatabaseConnection connection) {
        // 4. Inject it as a dependency.
        this.connection = connection;
    }

    public void performTask() {
        connection.connect(); 
    }
}

DatabaseConnection connection = new DatabaseConnection();
// You can also mock the connection in your tests

Service service = new Service(connection);
service.performTask(); Type [x]Semi-Automatic [x] Semi-Automatic [x] Safety This refactoring is safe when you update all references to the singleton and handle its dependencies correctly. Testing each step ensures that no references to the singleton are missed. Why Is the Code Better? Refactoring away from a singleton makes the code more modular, testable, and less prone to issues caused by the global state. Injecting dependencies allows you to easily replace DatabaseConnection with a mock or different implementation in testing and other contexts. Tags Coupling Coupling Related Refactorings https://maximilianocontieri.com/refactoring-007-extract-class?embedable=true https://maximilianocontieri.com/refactoring-007-extract-class?embedable=true See also https://hackernoon.com/singleton-pattern-the-root-of-all-evil-e4r3up7?embedable=true https://hackernoon.com/singleton-pattern-the-root-of-all-evil-e4r3up7?embedable=true https://hackernoon.com/coupling-the-one-and-only-software-designing-problem-9z5a321h?embedable=true https://hackernoon.com/coupling-the-one-and-only-software-designing-problem-9z5a321h?embedable=true Credits Image by PublicDomainPictures from Pixabay PublicDomainPictures Pixabay This article is part of the Refactoring Series. How to Improve Your Code With Easy Refactorings How to Improve Your Code With Easy Refactorings

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