Java OCA OCP Practice Question 1967

Question

How many times does the following application print Ready at runtime?. 

package mypkg; //from  w  ww .  java 2s . c  o  m

import java.util.concurrent.*; 

public class Main { 
   private void await(CyclicBarrier c) { 
      try { 
         c.await(); 
      } catch (Exception e) {} 
   } 
   public void march(CyclicBarrier c) { 
      ExecutorService s = Executors.newSingleThreadExecutor(); 
      for(int i=0; i<12; i++) 
         s.execute(() -> await(c)); 
      s.shutdown(); 
   } 
  public static void main(String... strings) { 
     new Main().march(new CyclicBarrier(4, 
           () -> System.out.println("Ready"))); 
  } 
}
  • A. Zero
  • B. One
  • C. Three
  • D. The code does not compile.


A.

Note

The code compiles without issue but hangs indefinitely at runtime.

The application defines a thread executor with a single thread and 12 submitted tasks.

Because only one thread is available to work at a time, the first thread will wait endlessly on the call to await().

Since the CyclicBarrier requires four threads to release it, the application waits endlessly in a frozen condition.

Since the barrier is never reached and the code hangs, the application will never output Ready, making Option A the correct answer.

If newCachedThreadPool() had been used instead of newSingleThreadExecutor(), then the barrier would be reached three times, and Option C would be the correct answer.




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