How does Object class implement clone() method

Question

In a book on Core Java, I found this excerpt :

Think about the way in which the Object class can implement clone. It knows nothing about the objec

Answer 1

Read this from the Javadoc:

protected Object clone() -

Creates and returns a copy of this object. The precise meaning of "copy" may depend on the class of the object. The general intent is that, for any object x, the expression:

x.clone() != x

will be true, and that the expression:

x.clone().getClass() == x.getClass()

will be true, but these are not absolute requirements. While it is typically the case that: x.clone().equals(x) will be true, this is not an absolute requirement. By convention, the returned object should be obtained by calling super.clone. If a class and all of its superclasses (except Object) obey this convention, it will be the case that

x.clone().getClass() == x.getClass().

By convention, the object returned by this method should be independent of this object (which is being cloned).

To achieve this independence, it may be necessary to modify one or more fields of the object returned by super.clone before returning it. Typically, this means copying any mutable objects that comprise the internal "deep structure" of the object being cloned and replacing the references to these objects with references to the copies. If a class contains only primitive fields or references to immutable objects, then it is usually the case that no fields in the object returned by super.clone need to be modified.

Means when you have a subobject in your object you shouldnt just clone/copy its reference but the internal structure of this object (in order to create a new instance of it), if each object has its clean clone() methode you will be able to clone it like the parent object otherwise you will have to create a new instance of it and copy its internal premitive fields one by one.

Answer 2

Actually, clone() is implemented in native code, so I assume it just does a memory copy (copy all the bytes) without knowing the contents.

Besides that, there is the Reflection API to gain knowlegde about a class (which would be slower, however).