Extending Classes - The Java Programming Language - page 151

3.9. Cloning Objects
The Object.clone method helps you write clone methods for your own
classes. A clone method returns a new object whose initial state is a copy
of the current state of the object on which clone was invoked. Subse-
quent changes to the new clone object should not affect the state of the
original object.
3.9.1. Strategies for Cloning
There are three important factors in writing a clone method:
• The empty Cloneable interface, which you must implement to
provide a clone method that can be used to clone an object. [3]
[3] Cloneable should have been spelled Clonable , but the misspelling was realized too late to
be fixed.
• The clone method implemented by the Object class, which per-
forms a simple clone by copying all fields of the original object to
the new object. This method works for many classes but may need
to be supplemented by an overriding method.
• The CloneNotSupportedException , which can be used to signal that a
class's clone method shouldn't have been invoked.
A given class can have one of four different attitudes toward clone :
• Support clone . Such a class implements Cloneable and declares its
clone method to throw no exceptions.
• Conditionally support clone . Such a class might be a collection
class that can be cloned in principle but cannot successfully be
cloned unless its contents can be cloned. This kind of class will im-
plement Cloneable , but will let its clone method pass through any