How to use Parallel Streams in Java?

Java 11 Certification Practice Questions (For the complete list, refer to

http://talks.skilltoz.com/java-11-certification-exam-questions/

Topic: Working with Streams and Lambda expressions

Objective: Perform decomposition and reduction, including grouping and partitioning on sequential and parallel streams

Questions

Q1. Which statements are true about the following code? (Choose all that apply.)

 Set<Integer> mySet = Set.of(5, 2, 8, 10);
   synchronized (mySet) {
      Integer num = mySet
                .parallelStream()
                .sorted()
                .findAny()
                .get();
      System.out.println("Num is " + num);
   }  

A. The first value printed will be 5
B. The first value printed will be 2
C. The code will not compile
D. The output cannot be determined ahead of time
E. The code compiles but throws an exception at runtime

Answers

Q1. Choice D is correct. The code compiles and runs without compile time or runtime issues, but the output cannot be predicted. The findAny() method finds any element from a Stream without considering the order. For parallel streams, findAny() method will return the value from the first thread that retrieves a record. Even if sort() is invoked on the parallel stream, findAny() method might not return the first record.

To learn more about parallel streams, check out

http://talks.skilltoz.com/all-about-parallel-streams

https://docs.oracle.com/javase/tutorial/collections/streams/parallelism.html