singleton and public static variable Java

Question

I have 2 options:

1. Singleton Pattern

   class Singleton{
       private static Singleton singleton = null;
   
       public static synchronized Singleton getInstance(){
           if(singleton  == null){
               singleton = new Singleton();
           }
           return singleton;
       }
   }
   

2. using a static final field

   private static final Singleton singleton = new Singleton();
   
   public static Singleton getSingleton() {
       return singleton;
   }
   

Whats the difference? (singlethreaded or multithreaded)

Updates: I am aware of Bill Pugh or enum method. I am not looking for the correct way, but I have only used 1. Is there really any difference b/w 1 or 2?

Answer 1

The main difference is that with the first option , the singleton will only be initialised when getInstance is called, whereas with the second option, it will get initialized as soon as the containing class is loaded.

A third (preferred) option which is lazy and thread safe is to use an enum:

public enum Singleton {
    INSTANCE;
}