Re: Thread safety, "array of singletons".

From:
"Daniel Pitts" <googlegroupie@coloraura.com>
Newsgroups:
comp.lang.java.programmer
Date:
25 Mar 2007 15:18:07 -0700
Message-ID:
<1174861087.574432.150890@o5g2000hsb.googlegroups.com>
On Mar 25, 2:58 pm, Tom Hawtin <use...@tackline.plus.com> wrote:

Daniel Pitts wrote:

I have a "Card" class which has objects that represent cards out of a
standard poker deck. I statically initialize the array.

My basic question is: Are there circumstances in which the following
code will not produce "==" comparable Card objects? These objects may
be passed through RMI or otherwise serialized.


I believe, malicious code could grab a deserialised instance before
readResolve, but other than that I think you have covered all the bases.

I'm not worried about malicious code in this place. the value only
"really" matters on a server side, which shouldn't load or execute
untrusted code at all. But out of curiosity, how WOULD malicious code
obtain a pre-readResolved reference? It doesn't matter in this case,
but if its possible, I should learn about it :-)

import java.io.InvalidObjectException;
import java.io.ObjectStreamException;

public final class Card {
  static final long serialVersionUID = 1L;


You mean:

public final class Card implements java.io.Serializable {
     private static final long serialVersionUID = 1L;

Yes I did.

  public final transient Suit suit;
  public final transient String number;
  public final transient int value;


I would calculate these on demand.

Perhaps, but I'm avoiding getters here, and there seems little reason
to not pre-calculate these values.

  protected final Object clone() throws CloneNotSupportedException {
    throw new CloneNotSupportedException();
  }


The class is final, so why bother?

Why bother? Just in case :-) Defensive programmming...
Having it declared this way lets future developers know it should not
be changed. This is actually noted in a comment that I stripped out.
It is also stolen from java.lang.Enum;

  protected final Object readResolve() throws ObjectStreamException {


Why protected?


Well, my IDE complains about unused private methods, and public seems
a bad idea, as well as package-protected.

Anyway, other than malicious readResolve interceptors, this looks like
it would be safe and correct code?

Thanks,
Daniel.

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