//: CheckCloneable.java
//////////////////////////////////////////////////
// Copyright (c) Bruce Eckel, 1998
// Source code file from the book "Thinking in Java"
// All rights reserved EXCEPT as allowed by the
// following statements: You can freely use this file
// for your own work (personal or commercial),
// including modifications and distribution in
// executable form only. Permission is granted to use
// this file in classroom situations, including its
// use in presentation materials, as long as the book
// "Thinking in Java" is cited as the source.
// Except in classroom situations, you cannot copy
// and distribute this code; instead, the sole
// distribution point is http://www.BruceEckel.com
// (and official mirror sites) where it is
// freely available. You cannot remove this
// copyright and notice. You cannot distribute
// modified versions of the source code in this
// package. You cannot use this file in printed
// media without the express permission of the
// author. Bruce Eckel makes no representation about
// the suitability of this software for any purpose.
// It is provided "as is" without express or implied
// warranty of any kind, including any implied
// warranty of merchantability, fitness for a
// particular purpose or non-infringement. The entire
// risk as to the quality and performance of the
// software is with you. Bruce Eckel and the
// publisher shall not be liable for any damages
// suffered by you or any third party as a result of
// using or distributing software. In no event will
// Bruce Eckel or the publisher be liable for any
// lost revenue, profit, or data, or for direct,
// indirect, special, consequential, incidental, or
// punitive damages, however caused and regardless of
// the theory of liability, arising out of the use of
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// and the publisher have been advised of the
// possibility of such damages. Should the software
// prove defective, you assume the cost of all
// necessary servicing, repair, or correction. If you
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// address for non-code errors found in the book.)
/////////////////////////////////////////////////
// Checking to see if a handle can be cloned
// Can't clone this because it doesn't
// override clone():
class Ordinary {}
// Overrides clone, but doesn't implement
// Cloneable:
class WrongClone extends Ordinary {
public Object clone()
throws CloneNotSupportedException {
return super.clone(); // Throws exception
}
}
// Does all the right things for cloning:
class IsCloneable extends Ordinary
implements Cloneable {
public Object clone()
throws CloneNotSupportedException {
return super.clone();
}
}
// Turn off cloning by throwing the exception:
class NoMore extends IsCloneable {
public Object clone()
throws CloneNotSupportedException {
throw new CloneNotSupportedException();
}
}
class TryMore extends NoMore {
public Object clone()
throws CloneNotSupportedException {
// Calls NoMore.clone(), throws exception:
return super.clone();
}
}
class BackOn extends NoMore {
private BackOn duplicate(BackOn b) {
// Somehow make a copy of b
// and return that copy. This is a dummy
// copy, just to make the point:
return new BackOn();
}
public Object clone() {
// Doesn't call NoMore.clone():
return duplicate(this);
}
}
// Can't inherit from this, so can't override
// the clone method like in BackOn:
final class ReallyNoMore extends NoMore {}
public class CheckCloneable {
static Ordinary tryToClone(Ordinary ord) {
String id = ord.getClass().getName();
Ordinary x = null;
if(ord instanceof Cloneable) {
try {
System.out.println("Attempting " + id);
x = (Ordinary)((IsCloneable)ord).clone();
System.out.println("Cloned " + id);
} catch(CloneNotSupportedException e) {
System.out.println(
"Could not clone " + id);
}
}
return x;
}
public static void main(String[] args) {
// Upcasting:
Ordinary[] ord = {
new IsCloneable(),
new WrongClone(),
new NoMore(),
new TryMore(),
new BackOn(),
new ReallyNoMore(),
};
Ordinary x = new Ordinary();
// This won't compile, since clone() is
// protected in Object:
//! x = (Ordinary)x.clone();
// tryToClone() checks first to see if
// a class implements Cloneable:
for(int i = 0; i < ord.length; i++)
tryToClone(ord[i]);
}
} ///:~ |