java - Behavoir of Threads with AtomicInteger -

the following problem on mock exam ocp java se 7 programmer ii exam. solution says answer 0, colleagues , not sure answer isn't between -5 , 5 (which choice) clarify us? here code:

import java.util.concurrent.atomic.atomicinteger; class atomicvariabletest {         private static atomicinteger counter = new atomicinteger(0);         static class decrementer extends thread {                 public void run() {                         counter.decrementandget(); // #1                 }          }         static class incrementer extends thread {                 public void run() {                         counter.incrementandget(); // #2                 }          }         public static void main(string []args) {                 for(int = 0; < 5; i++) {                         new incrementer().start();                         new decrementer().start();                 }                 system.out.println(counter);          } } 

thanks!

running multiple times logs shows order in threads ran change outcome. on multiple runs, did 0, results experimentally varied -1 2 on machine. valid answer : between -5 , 5.

class atomicvariabletest {     private static atomicinteger counter = new atomicinteger(0);      static class decrementer extends thread     {         public void run()         {             counter.decrementandget(); // #1             system.out.println("dec");         }     }      static class incrementer extends thread     {         public void run()         {             counter.incrementandget(); // #2             system.out.println("inc");         }     }      public static void main(string[] args)     {         (int = 0; < 5; i++)         {             new incrementer().start();             new decrementer().start();         }         system.out.println(counter);     } } 

output of program looking :

inc dec inc dec inc dec inc dec 0 inc dec 

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dec -1 inc dec inc dec dec dec inc inc inc