Singleton Design Pattern ¶

Aliases 📌: None

Description 📚: the singleton is used to only have one instance of a class. It's a sort of global variable that we usually access by calling a method #getInstance() from the singleton class.

• Lazy instantiation: initialization of the global variable when requesting the instance

• Early instantiation: initialization of the global variable when declaring it

Advantages ✅

• Lower memory usage and consumption
• Centralizing a global point of access to a variable

Disadvantages 🚫

• Instances are shared/global so it increase complexity

Notes 📝

• Commonly used for Utility Classes

Lazy instantiation ¶

public class RpgMaker {
    private static RpgMaker instance = null;

    // get instance, lazy instantiation
    public static RpgMaker getInstance() {
        // creates
        if(instance == null) instance = new RpgMaker();
        return instance;
    }

    // private !!!
    private RpgMaker(){}
}

Early instantiation ¶

public class RpgMaker {
    // creates, early instantiation
    private static RpgMaker instance = new RpgMaker();

    // get instance
    public static RpgMaker getInstance() {
        return instance;
    }

    // private !!!
    private RpgMaker(){}
}