Singleton

Singleton pattern is mentioned in both good patterns and also in anti patterns. Why? I think because singleton is easy to implement and many people wanted to use design patterns where ever it is possible, even when they didn't have a need to solve an issue. Then we ended up with code that is:

• difficult to use

• complex

• difficult to test

Some people suggest that Singleton is an anti-pattern because it brings more evil than good. Still, Singleton pattern is useful when it is used correctly.

A lesson to learn here is "Use Singleton only when you face an issue, never just because you think it might make the code more cool or fancy".

Example of Singleton pattern

How to create an anti pattern of Singleton pattern? It should be easy. We just need to use Singleton pattern when we shouldn't use it.

public class UserFactory {

    private static UserFactory userFactory;

    private UserFactory() {
    }

    public static UserFactory getInstance() {
        if (userFactory == null) userFactory = new UserFactory();
        return userFactory;
    }

    public User createUser(String name) {
        return new User(name);
    }
}

class User {
    String name;

    public User(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

class Main {
    public static void main(String [] args) {
        User john = UserFactory.getInstance().createUser("John");
        System.out.println(john.getName());
    }
}

There is no reason why a developer who is using this this code couldn't create an instance of User class by him self. The code above seems to be over-engineered.