Java OCA OCP Practice Question 3071

Question

Consider the following program and choose the correct option: 

import java.util.concurrent.atomic.AtomicInteger;

public class Main {
   private static AtomicInteger counter = new AtomicInteger(0);

   static class Decrementer extends Thread {
      public void run() {
         counter.decrementAndGet(); // #1
      }/*from  www.  j a  va2s.c  o  m*/
   }

   static class Incrementer extends Thread {
      public void run() {
         counter.incrementAndGet(); // #2
      }
   }

   public static void main(String[] args) {
      for (int i = 0; i < 5; i++) {
         new Incrementer().start();
         new Decrementer().start();
      }
      System.out.println(counter);
   }
}

a)this program will always print 0
b)this program will print any value between -5 to 5
c)If you make the run() methods in the Incrementer and 
  Decrementer classes synchronized, this program will always print 0
d)the program will report compilation errors at statements #1 and #2



b)

Note

You have employed AtomicInteger, which provides a set of atomic methods such as incrementAndGet() and decrementAndGet().

hence, you will always get 0 as the final value of counter.

however, depending on thread scheduling, the intermediate counter values may be anywhere between -5 to +5, hence the output of the program can range between -5 and +5.




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