Cloneable

Cloneable Interface in Java

30 Nov 2012

This post will give some deep insight into Cloneable Interface in Java.

A  clone of an object is an object with distinct identity and equal contents. To define clone, a class must implement cloneable interface and must override Object’s clone method with a public modifier. At this point, it is worth nothing that cloneable interface does not contain the clone method, and Object’s clone method is protected.

When the Object class finds that the object to be cloned isn’t an instance of a class that implements cloneable interface, it throws CloneNotSupportedException.

If a class wants to allow clients to clone it’s instances, it must override Object’s clone method with a public modifier.

Now let’s look into the details of how to implement clone method.

If you override the clone method in a non final class, you should return an object obtained by invoking super.clone. If all of a class’s super classes obey this rule, then invoking super.clone will eventually invoke Object’s clone method, creating an instance of the right class.

A small example, if classes don’t obey this rule.

Once you get hold of object from super.clone(), we may have to do some modifications depending on nature of the class If every field contains a primitive value or a reference to an immutable object, no further processing is necessary. If there are references to mutable objects, in order to work clone properly, it is required to call clone on those mutable references.

Example to clone mutable references

If there are  final fields referring to mutable objects,  In order to make a class cloneable, it may be necessary to remove final modifiers from some fields. If you decide to make a thread-safe class implement Cloneable, remember that its clone method must be properly synchronized just like any other method

Final Note: Implementation of clone is very tricky. Avoid implementing it and look for other alternatives.