Greetings.

I'd like to define a wrapper class, whose instances keep read-only
copies of the original object passed in. I tried using generics for this:

public class RestorableObject<T> {

 private T original;
 private T workingCopy;

 public RestorableObject(T obj) {
   original = obj;
   workingCopy = obj.clone();  // clone() is protected in Object
 }

}

After RTFM on how generics actually work, the error message is explainable:
T is unbounded, so the compiler sees me calling a protected method outside
of its class.

So here is my next attempt:

public class RestorableObject<T extends Cloneable> {

 private T original;
 private T workingCopy;

 public RestorableObject(T obj) {
   original = obj;
   workingCopy = obj.clone();  // clone() not found in Cloneable
 }

}

I should have seen this coming, since Cloneable is an empty interface,
and the docs state that

* By _convention_, classes that implement this interface should override
* Object.clone (which is protected) with a public method.

I guess nobody told javac about this _convention_ ... must be human thing.

I would like to make the compiler ensure that RestorableObject is
only wrapped around objects providing a clone() method. I can do
this by introducing an interface

public interface ReallyCloneable<T> {
 public T clone();
}

and finally arriving at

public class RestorableObject<T extends ReallyCloneable<T>> {
 
 private T original;
 private T current;
 
 public RestorableObject(T obj) {
   original = obj;
   current = obj.clone();
 }
 
}

Is there a more elegant way of doing this?

Regards,
Stefan