A possible typo in question (or answer) 36 in chapter 9 (OCP 17 - Practice Tests)

[Albert Attard]

Hello

With reference to question 36 in chapter 9 of the OCP Oracle Certified Professional Java SE 17 Developer Practice Tests: Exam 1Z0-829 (English Edition) book (Kindle edition), shown below.

In this question, an instance of Cereal has been serialized to disk, with the source object having a name value of CornLoops and sugar value of 5. What is the value of name and sugar after this object has been read from disk using the ObjectInputStream's readObject() method?

The question seems to start with a fact: "In this question, an instance of `Cereal` has been serialized to disk...".  The Bowl record does not implement Serializable, which means the bowl instance field must have been null (otherwise the initial part of the question is incorrect).  

Given that the bowl instance field must have been null during serialisation, we are able to deserialize the object, making option B correct.  Following are all options available for completeness.

A. CaptainPebbles and 10
B. CornLoops and 0
C. SugarPops and 10
D. SugarPops and 2
E. CornLoops and -1
F. None of the above

Any thoughts?

[Stephan van Hulst]

If you want our thoughts, you'll have to share more context. We don't know what the Cereal class (or any of its components) looks like, nor what the question is asking.

[Albert Attard]

Thank you for your reply.

I made the wrong assumption that everyone in this chat group has the book.

This is the Cereal class.

package breakfast;
import java.io.Serializable;
record Bowl (boolean spoon) {}
public class Cereal implements Serializable {
  private String name = "CocoaCookies";
  private transient int sugar = 10;
  private Bowl bowl;
  public Cereal () {
	super ();
	this.name = "CaptainPebbles";
	this.bowl = new Bowl(true);
	sugar = 2;
  }
  { name = "SugarPops"; }

  public void setName(String name) {
	this.name = name;
  }

  public void setSugar(int sugar) {
	this.sugar = sugar;
  }

  public void setBowl(Bowl bowl) {
	this.bowl = bowl;
  }

  @Override
  public String toString() {
	return "Cereal[name=%s, sugar=%d, bowl=%s]".formatted(name, sugar, bowl);
  }
}

I have added the setters and toString() methods as these were omitted, I believe for brevity.

The following code shows how to reproduce this.

    	Cereal a = new Cereal();
    	a.setBowl(null);
    	a.setName("CornLoops");
    	a.setSugar(5);

    	try (var oos = new ObjectOutputStream(new FileOutputStream("./cereal.data"))) {
        	oos.writeObject(a);
    	}

    	try (var ois = new ObjectInputStream(new FileInputStream("./cereal.data"))) {
        	Cereal b = (Cereal) ois.readObject();
        	System.out.println(b);
    	}

The above example works and prints the output matching option B.

[Stephan van Hulst]

Okay, so what's the problem?

[Albert Attard]

I believe the answer is incorrect.

The book says option F is the correct answer, while I believe it should be option B.

[Jeanne Boyarsky]

Ok that one gets TWO cows. Added to errata.

You broke our question . Seriously though, you are right. We were not assuming it would be null. But then it fails on writing rather than reading and that breaks the question.