Re: Thread safety, "array of singletons".

"Daniel Pitts" <>
25 Mar 2007 15:18:07 -0700
On Mar 25, 2:58 pm, Tom Hawtin <> 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 :-)


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

You mean:

public final class Card implements {
     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?


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