question concerning clone() method

[sura watthana]

as mentioned earlier

Cloning means creating a new object based on another object. As said, they are 2 different objects that share the same value.

when object B is cloned from object A.
then later after the execution of the programme, object A changes its properties or behaviour or both. My question is, will object B change too?

Thanks

Sura

[JayaSiji Gopal]

hi,

i guess changes in object A will automatically be reflected in object B. since B is a cloned instance of A.

others plz comment?

[Anthony Villanueva]

Originally posted by sura watthana:
when object B is cloned from object A.
then later after the execution of the programme, object A changes its properties or behaviour or both. My question is, will object B change too?

Yes. clone() performs a shallow copy, meaning only object references are copied but these object references in objects A and B both point to the same objects.

[Kai Witte]

hello,

technically the answers are correct. But clone() should be implemented in such a way that changes in one object are not reflected by the other one. A typical way to override Object#clone() is to call super.clone() and then "fix" those fields that would otherwise cause this reflection.

public class MovieDB implements Cloneable {
    private List<String> movies = new ArrayList<String>();
 
    //...
    
    public Object clone() {
        MovieDB ret;
        try {
            ret = (MovieDB) super.clone();
        } catch (CloneNotSupportedException e) {
            // can't happen
            throw new RuntimeException();
        }
        ret.movies = new ArrayList<String>(movies); // "fix" List
        return ret;
    }
}

Recommended reading: Effective Java, Chapter 3

Conan

[Jeroen Wenting]

correct. Clone() SHOULD make a deep copy of your object, but the compiler cannot do that on its own so only copies object references and not the referenced objects.

To put it simply, a deep copy is made of the references when what you'd want is to create new references to clones (however deep it goes) of all referenced objects.

[kapil munjal]

Hi,

Is clone() covered in SCJP???

May be I have not gone through this topic, could you tell me, to which topic it is concerned???

Thanks
Kap

[sura watthana]

yes clone() is covered in SCJP exam.

[sura watthana]

yes, method clone() is covered in SCJP 1.4 exam.
The topic concerned is the "Object" class.

hope this helps
Sura

[Robert Chisholm]

Never got a clone question in the Dan Chisholm mocks. Never saw the topic covered in the K&B book. Never saw the question on the exam.

[Bert Bates]

Robert's correct!

You can relax on this one, the SCJP 1.4 exam does NOT cover the clone() method!

Yeah! Of course, it's good to understand clone(), but if you're just focusing on the exam you can put your precious study time to use in other areas. The areas that are typically the best places to put your emphasis are:

THREADS
INNER CLASSES
GARBAGE COLLECTION

There will be lots of questions on these topics, and they're pretty tricky!

Someone might do a search on an old topic from this forum entitled something like:

"Top ten things people think are on the exam, but aren't"

If you find it, resurrect it!

Thanks,

Bert

[kapil munjal]

Hey friends,

check this out..........

Top ten to top 100%

well, I found it through search on this forum......

Thanks Bert.....