Clone Method

[Arjun Reddy]

Hi All,

I am working on clone method and I was wondering if we have to always override it in order to use it? I've seen some places online where the method has been overridden but for me, without even overriding it, My code works fine?! I am cloning a sample class's object and not classes like ArrayList who have already overridden the clone method.

Thanks.
[ September 07, 2008: Message edited by: Arjun Reddy ]

[arulk pillai]

You should override the clone() method very judiciously. Implementing a properly functioning clone method is complex and it is rarely necessary. You are better off providing some alternative means of object copying like serializing and deserializing (could have a performance impact), static factory method or simply not providing the capability. A better approach is to provide a copy constructor or a static factory method in place of a constructor.

//constructor
public Pet(Pet petToCopy){
     �
}
 
//static factory method
public static Pet newInstance(Pet petToCopy){
     �
}
 
The clone() method can be disabled as follows:
 
public final Object clone() throws CloneNotSupportedException {
    throw new CloneNotSupportedException();
}

Static factory method

   
to deep copy a list of Car objects.
 
public static List deepCopy(List listCars) {
     List copiedList = new ArrayList(10);
     for (Object object : listCars) {   //JDK 1.5 for each loop
        Car original = (Car)object;
        Car carCopied = new Car();  //instantiate a new Car object
        carCopied.setColor((original.getColor()));
        copiedList.add(carCopied);
    }
    return copiedList; 
}
 

[ September 07, 2008: Message edited by: arulk pillai ]

[Arjun Reddy]

So, the following clone method program is wrong? coz am not overriding the clone method?

public class CloneMethodTest implements Cloneable {
int i=10;
void somemethod()
{

}
public static void main(String[] args) {
CloneMethodTest obj = new CloneMethodTest();
 
try {
CloneMethodTest clonedobj = (CloneMethodTest)obj.clone();
}
catch (CloneNotSupportedException e) {
e.printStackTrace();
}
 

}
 
}

Thanks.

[Ankit Garg]

If you implement the Cloneable interface, then the clone method of Object class will create a SHALLOW copy of your object, but if you don't implement the Cloneable interface, then the clone method of the object class throws CloneNotSupported exception.

If you want complete control over cloning your objects, then you must implement the Cloneable interface and override the clone method of the object class..

[Patricia Samuel]

That means if we need a shallow copy of an object we don't need to override clone method as shown in the above post??

But if we need a deep copy then only we would override the clone method??

Kindly clarify.

[Bert Bates]

this is an interesting discussion, and for those of you keeping score, this topic is NOT on any version of the SCJP exam.

hth,

Bert

[Patricia Samuel]

Would anyone like answer my previous post?

[Ankit Garg]

@Patricia you must override clone method if you need complete control over the cloning process. Also note that clone method in Object class is protected. So if you implement Cloneable interface and don't override clone method, no code outside the class will be able to call clone on the object of your class.

So basically to implement cloning you must override the clone method.

And as Bert said, it is not a part of SCJP so if you are only concerned with SCJP, you need not to worry about cloning...

[Patricia Samuel]

Ah!! I missed this point. I tried an example using main method. I forgot that in real application, we have to use it outside the class.

Thanks Ankit.