best way to use a Singleton in Java

Question

Assuming that we have a thread safe singleton class in Java, which would be the best or better way to use it. For instance, consider that we have a Singleton class as:

public class MySingleTon {
   // my thread-safe code goes here
}

And we have a service class that uses the above singleton in the two possible ways as follows :

1:

public class MyService {
   MySingleton singleton;

   public void myMethod1() {
      singleton  = MySingleton.getInstance();
      // code ...
   }

   public void myMethod2() {
      singleton = MySingleton.getInstance();
      // code...
   }
   public void myMethod3() {
      singleton = MySingleton.getInstance();
      // code...
   }
}

or

2:

public class MyService {

   public void myMethod1() {
      MySingleton singleton = MySingleton.getInstance();
      // code ...
   }

   public void myMethod2() {
      MySingleton singleton = MySingleton.getInstance();
      // code...
   }
   public void myMethod3() {
      MySingleton singleton = MySingleton.getInstance();
      // code...
   }
}

In case one the singleton is referenced via an instance variable and in case 2, the singleton is referenced as a method local variable. Considering that both the above snippets are used in multi-threaded environment, which is a better option and why?

Answer 1

I would define it a third way

public class MyService {
   final static MySingleton singleton = MySingleton.getInstance();

   public void myMethod1() {
      // code ...
   }

   public void myMethod2() {
      // code...
   }
   public void myMethod3() {
      // code...
   }
}

In all cases there is no difference in thread-safety