Java OCA OCP Practice Question 2838

Question

What statement about the following code is true? 

import java.util.concurrent.atomic.AtomicLong;
import java.util.stream.IntStream;

public class Main {

   public static void main(String[] args) {
      AtomicLong value1 = new AtomicLong(0);
      final long[] value2 = { 0 };

      IntStream.iterate(1, i -> 1).limit(100).parallel().forEach(i -> value1.incrementAndGet());
      IntStream.iterate(1, i -> 1).limit(100).parallel().forEach(i -> ++value2[0]);
      System.out.println(value1 + " " + value2[0]);

   }/* w w  w.j a va  2s .co  m*/
}
  • A. It outputs 100 100.
  • B. It outputs 100 99.
  • C. The output cannot be determined ahead of time.
  • D. The code does not compile.
  • E. It compiles but throws an exception at runtime.
  • F. It compiles but enters an infinite loop at runtime.


C.

Note

The code compiles and runs without throwing an exception or entering an infinite loop, so D, E, and F are incorrect.

The key here is that the increment operator ++ is not atomic.

While the first part of the output will always be 100, the second part is nondeterministic.

It could output any value from 1 to 100, because the threads can overwrite each other's work.

Therefore, C is the correct answer and A and B are incorrect.




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