Multiton Design Pattern ¶

Aliases 📌: None

Description 📚: This pattern is a generalization of the singleton pattern with n instances instead of 1.

Advantages ✅

• Same as a singleton

Disadvantages 🚫

• Same as a singleton

Notes 📝

• We use getInstance(xxx) with xxx something to identify which instance you want (ex: an int, a string...).

Lazy instantiation ¶

public class RpgMaker {
    private static final int MAX_INSTANCE = 5;
    private static ArrayList<RpgMaker> instance = null;

    // get instance
    public static RpgMaker getInstance(int i) {
        if (i > MAX_INSTANCE || i < 0) throw new IllegalArgumentException("not a valid key");
        if (instance == null) {
            // initialization
            instance = new ArrayList<>();
            // fill the list
            for (int j = 0; j < MAX_INSTANCE; j++) {
                instance.add(new RpgMaker());
            }
        }
        return instance.get(i);
    }

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

Early instantiation ¶

public class RpgMaker {
    private static final int MAX_INSTANCE = 5;
    // initialization
    private static final ArrayList<RpgMaker> instance = new ArrayList<>();
    static {
        // fill the list
        for (int j = 0; j < MAX_INSTANCE; j++) {
            instance.add(new RpgMaker());
        }
    }

    // get instance
    public static RpgMaker getInstance(int i) {
        if (i > MAX_INSTANCE || i < 0) throw new IllegalArgumentException("not a valid key");
        return instance.get(i);
    }

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