Java OCA OCP Practice Question 2675

Question

Consider the following code and choose the best option: 

import java.util.concurrent.atomic.AtomicInteger;

class Main {/*from  w  w w. j a va2s.  c  om*/
       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 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.


a)

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, but the final value of the counter will always be 0.

So no synchronization is needed between the threads, although they access/modify a common variable.




PreviousNext

Related