Overriding clone with and without Cloneable

Question

I've read the javadoc for both Object and Cloneable and am just not "getting" something. Can someone please explain to me the performance and/or functional differences to the two following examples:

public class Widget
{
    @Override
    public Widget clone()
    {
            // ... return a clone of this Widget
    }
}

..and:

public class Widget implements Cloneable
{
    @Override
    public Widget clone()
    {
            // ... return a clone of this Widget
    }
}

Since Cloneable does not have any methods tied to it, and only gives you access to Object's protected clone() method, does it ever make sense to even implement it in the first place, seeing that you're going to have to end up writing your own (safe) clone() code any way? Thanks in advance for any clarification/input.

Aaron McIver · Accepted Answer · 2011-10-14T19:11:12.257

It's a contractual obligation.

Invoking Object's clone method on an instance that does not implement the Cloneable interface results in the exception CloneNotSupportedException being thrown.

While there may be no methods to override, you are still implementing an interface you are part of. In doing this you take on all that comes with its subsequent contract. It forces you to knowingly implement the clone() method thus making the behavior explicit.

score 0 · Answer 2 · edited May 23 '17 at 10:26

a) Cloning invokes extralinguistic way of constructing objects - without constructors.

b) Cloning requires you to treat somehow with CloneNotSupportedException - or to bother client code for treating it.

c) Benefits are small - you just don't have to write manually a copying constructor. So, use Cloneable judiosly. It doesn't give you suffisient benefits in compare with effort you need to apply to do all right.

About Java cloneable

Overriding clone with and without Cloneable

2 Answers2