CODESAMPLE

Multiton - Java

Multiton Java

The Multiton pattern ensures that only a limited number of instances of a class exist. It’s a relaxation of the Singleton pattern, useful when more than one object is needed but a full-blown factory feels excessive. This Java implementation uses an enum to define the limited set of instances, leveraging the inherent guarantee that enum values are instantiated only once. The enum approach is concise and thread-safe, aligning with Java’s preference for enums when a fixed set of constants with associated state is required, making it more idiomatic than explicit static instance management.

// Multiton.java
public class Multiton {

    private final String value;

    private Multiton(String value) {
        this.value = value;
    }

    public String getValue() {
        return value;
    }

    public enum Instance {
        INSTANCE_ONE("First"),
        INSTANCE_TWO("Second"),
        INSTANCE_THREE("Third");

        private final Multiton multiton;

        Instance(String value) {
            this.multiton = new Multiton(value);
        }

        public Multiton getInstance() {
            return multiton;
        }
    }

    public static void main(String[] args) {
        Multiton instance1 = Multiton.Instance.INSTANCE_ONE.getInstance();
        Multiton instance2 = Multiton.Instance.INSTANCE_TWO.getInstance();
        Multiton instance3 = Multiton.Instance.INSTANCE_THREE.getInstance();

        System.out.println(instance1.getValue());
        System.out.println(instance2.getValue());
        System.out.println(instance3.getValue());

        // Verify that instances are unique
        System.out.println(instance1 == instance2); // false
        System.out.println(instance1 == instance3); // false
        System.out.println(instance2 == instance3); // false
    }
}