Why is the clone() method protected in java.lang.Object?

clone, java, oop

Solution

The fact that clone is protected is extremely dubious - as is the fact that the `clone` method is not declared in the `Cloneable` interface.

It makes the method pretty useless for taking copies of data because you cannot say:

if(a instanceof Cloneable) {
    copy = ((Cloneable) a).clone();
}

I think that the design of `Cloneable` is now largely regarded as a mistake (citation below). I would normally want to be able to make implementations of an interface `Cloneable` but not necessarily make the interface `Cloneable` (similar to the use of `Serializable`). This cannot be done without reflection:

ISomething i = ...
if (i instanceof Cloneable) {
   //DAMN! I Need to know about ISomethingImpl! Unless...
   copy = (ISomething) i.getClass().getMethod("clone").invoke(i);
}

Citation From Josh Bloch's Effective Java: "The Cloneable interface was intended as a mixin interface for objects to advertise that they permit cloning. Unfortunately it fails to serve this purpose ... This is a highly atypical use of interfaces and not one to be emulated ... In order for implementing the interface to have any effect on a class, it and all of its superclasses must obey a fairly complex, unenforceable and largely undocumented protocol"

Problem

Original source