java - Singleton with Enum called by threads -

hi can 1 me understand output of below snippet?

enum -

public enum singletonenum {   instance;   int num;    public void demo(){     system.out.println(num);   } } 

main class -

public static void main(string[] args) {             thread t1 = new thread(new runnable(){         public void run(){             singletonenum samp = singletonenum.instance;             samp.num= 5;             samp.demo();         }     });      thread t2 = new thread(new runnable(){         public void run(){             singletonenum temp = singletonenum.instance;             temp.num= 8;             temp.demo();         }     });     t1.start();     t2.start();      } 

the o/p 8 , 8 .however if add private constructor in enum o/p 5 , 8. logic behind o/p being 8 , 8.

you code not synchronized. unspecified behavior, can observe in such case.