Deep copy of complicated object

[Ismael Upright]

Hi there,

Assume that you have an object A.

It contains many objects.

Some of these objects are ArrayLists of another objects

Soem of those objects from the ArrayLists are also ArrayLists.

Etc.


In short: you have an objects containing objects which may be ArrayLists that contains object which may be ArrayLists etc.


How would you make a deep copy B of such object A?

A deep copy = no common references between the contains of the object A and the contains of the object B which is a copy of object A.

[Ernest Friedman-Hill]

One trick you can use is to serialize the object tree, then reload it to create the copy.

[Campbell Ritchie]

Originally posted by Ernest Friedman-Hill:
One trick you can use is to serialize the object tree, then reload it to create the copy.

I think you will find more details in this article. Beware of serializing anything with passwords in, or singletons.

[Ismael Upright]

Thanks for your replies.

Isn't it that we can use this solution only if all objects in the object tree are serializable?

[Ernest Friedman-Hill]

Originally posted by Ismael Upright:
Thanks for your replies.

Isn't it that we can use this solution only if all objects in the object tree are serializable?

Yep.

There are other remaining alternatives, of course, which all boil down to explicitly writing code to walk through the tree of objects and copy everything. You can do this either by overriding clone() -- and thereby making use of clone() to do some of the work -- or by ignoring clone(), and writing your own code.

[Mike Simmons]

It's also possible to use reflection to systematically copy data from all fields of an object - even if the object is not serializable. I think there are several tools that do this already - the one I know best is XStream. You can use this to convert almost any object to a simple String representation (using XML, JSON, or other formats), then read that String and convert it to a new instance. While there are some classes it can't convert, it works pretty easily for most of them.

[Paul Clapham]

Originally posted by Ernest Friedman-Hill:
walk through the tree of objects

Also bear in mind that it's possible you don't have a tree of objects. In general you have a directed graph of objects. It's possible that two objects in this complicated thing both contain references to a third object. In that case you might well want the copies of those two objects to contain references to a single copy of the third object.

Serialization takes care of this issue.