SingletonTester.java

public class SingletonTester {
   public static void main(String[] args) {
        //Create the 1st instance
        SingletonClass instance1 = SingletonClass.getInstance();
        
        //Create 2nd instance using Java Reflection API.
        SingletonClass instance2 = null;
        try {
            Class<SingletonClass> clazz = SingletonClass.class;
            Constructor<SingletonClass> cons = clazz.getDeclaredConstructor();
            cons.setAccessible(true);
            instance2 = cons.newInstance();
        } catch (NoSuchMethodException | InvocationTargetException | IllegalAccessException | InstantiationException e) {
            e.printStackTrace();
        }

        //now lets check the hash key.
        System.out.println("Instance 1 hash:" + instance1.hashCode());
        System.out.println("Instance 2 hash:" + instance2.hashCode());
   }
}

This still is not fullproof as to What would happen if I create an instance of SingleTonClass first using reflection and then using getInstance.
This class allows me to create two instances in that case