Illustration of breaking Singleton pattern using Cloneable interface

SingletonCloningExample.java

/**
 * Using Cloneable Interface, we can create more than one instance in a Singleton class by
 * simply using the clone() on the first object
 */
public class SingletonCloningExample implements Cloneable {

    private static SingletonCloningExample single_instance = null;

    @Override
    protected Object clone() throws CloneNotSupportedException
    {
        return super.clone();
    }

    /**
     * Making the constructor as private
     */
    private SingletonCloningExample() {}

    /**
     * Static method to create instance of Singleton class
     * @return single object of 'SingletonCloningExample' class
     */
    public static SingletonCloningExample getInstance() {
        /**
         * Ensuring only one instance is created
         */
        if (single_instance == null)
            single_instance = new SingletonCloningExample();
        return single_instance;
    }

    public static void main(String[] args) throws CloneNotSupportedException {

        /**
         * Instantiating SingletonCloningExample class with variable 'objectOne'
         */
        SingletonCloningExample objectOne = SingletonCloningExample.getInstance();

        /**
         * Cloning the 'objectOne' using clone()
         */
        SingletonCloningExample objectTwo = (SingletonCloningExample) objectOne.clone();

        /**
         * Checking the hashCode for both the objects which would be different,
         * meaning the objects are different
         */
        System.out.println("Hashcode of Object 1 - " + objectOne.hashCode());
        System.out.println("Hashcode of Object 2 - " + objectTwo.hashCode());
    }

}