[jdom-interest] DocType equals()-hashCode() contract violation

[Jason Hunter]

I changed DocType.equals() to be solely reference equality.  As with the
other content objects in JDOM, we'll leave it up to the user to define
exactly what equality means.

-jh-

Elliotte Rusty Harold wrote:
> 
> The DocType class uses a custom equals() method but does not use a
> custom hashCode() method; i.e.
> 
>     public final boolean equals(Object ob) {
>         if (ob instanceof DocType) {
>             DocType dt = (DocType) ob;
>             return (stringEquals(dt.elementName, elementName) &&
>                     stringEquals(dt.publicID, publicID) &&
>                     stringEquals(dt.systemID, systemID));
>         }
>         return false;
>     }
> 
>     public final int hashCode() {
>         return super.hashCode();
>     }
> 
> Thus two equal DocType objects may have different hash codes. We need to
> fix one of these methods. Either equals() needs to return super.equals()
> or we need to calculate the hasCode based on the elementName, publicid,
> and systemID. I'm not sure which one to patch. My initial reation is to
> fix hashCode(). Thoughts? Either way this change should not break
> existing code.
> 
> Issue 2: Should we consider the internal DTD subset when comparing two
> DocTypes for equality (and when calculating the hash code)? My suspicion
> is we should. Two DocTypes with the same root element name can be very
> different if the internal DTD subset is different. The again they may be
> effectively the same modulo white space and other insignificances. Is it
> more important to ensure that two inequal DTDs are not reported as equal
> or that two equal DTDs are not reported as inequal?
> 
> --
> +-----------------------+------------------------+-------------------+
> | Elliotte Rusty Harold | elharo at metalab.unc.edu | Writer/Programmer |
> +-----------------------+------------------------+-------------------+
> |           The XML Bible, 2nd Edition (IDG Books, 2001)             |
> |             http://www.cafeconleche.org/books/bible2/              |
> |   http://www.amazon.com/exec/obidos/ISBN=0764547607/cafeaulaitA/   |
> +----------------------------------+---------------------------------+
> |  Read Cafe au Lait for Java News:   http://www.cafeaulait.org/     |
> |  Read Cafe con Leche for XML News:  http://www.cafeconleche.org/   |
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> 
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