java Singleton - prevent multiple creation through reflection

Question

I have a singleton like this.

public class BookingFactory {

    private final static BookingFactory instance;

    static {
        instance = new BookingFactor         


        

Answer 1

Try using an enum. enums make for good Singletons.

public static enum BookingFactory {
    INSTANCE;
    public static BookingFactory getInstance() {
        return INSTANCE;
    }
}

You can't create an enum via reflection.

The getInstance() method is superfluous but makes it easier to run your test, throwing the following exception:

java.lang.IllegalArgumentException: Cannot reflectively create enum objects
    at java.lang.reflect.Constructor.newInstance(Constructor.java:530)
    at MultiSingletonTest.main(MultiSingletonTest.java:40)

Oh look, someone already gave the enum answer. Posting anyway for more completeness.