Mutable, Immutable, and Cloneable Objects - Data Structures and Abstractions with Java - page 793

Programming Tip: When bounding generic types, use an interface that declares a pub-
lic method clone instead of using Cloneable . The new interface must extend Cloneable ,
however.

30.21

Using Copyable as a bound for T requires us to change the implementation of AList 's constructor.
Recall from Listing 13-1 in Chapter 13 that one field of AList is an array of list entries:
private T[] list;
Writing
list = (T[]) new Object[initialCapacity];
in the constructor causes a ClassCastException . Instead, we write
list = (T[]) new Copyable[initialCapacity];

30.22

Now we can implement clone . We will invoke super.clone() within a try block but perform the
rest of the tasks after the catch block. Thus, we have the following outline for AList 's method clone :

public Object clone()
{

AList<T> theCopy = null ;
try
{

theCopy = (AList<T>) super .clone(); // not enough by itself

}
catch (CloneNotSupportedException e)
{

throw new Error(e.toString());

}
< For a deep copy, we need to do more here, as you will see. >
. . .
return theCopy;
} // end clone
The method first invokes super.clone and casts the returned object to AList<T> . To perform a
deep copy, we need to clone the data fields that are or could be mutable objects. Thus, we need to
clone the array list .

30.23

Arrays in Java have a public clone method; in other words, they implement Cloneable . So we can
add the following statement to the list's clone method:
theCopy.list = (T[])list.clone();
No try and catch blocks are necessary here.
An array's clone method creates a shallow copy of each object in the array. For our deep copy,
we need to clone each array entry. Since we insisted that the list's entries have a public clone
method, we can write a loop whose body contains the following statement:
theCopy.list[index] = (T)list[index].clone();
We can control the loop by using AList 's data field numberOfEntries , which records the number of
entries in the list.
Thus, we have the following definition of clone for the class AList :
public Object clone()
{

AList<T> theCopy = null ;