* Matthew Toseland <toad at amphibian.dyndns.org> [2008-04-04 19:13:51]:
> On Friday 04 April 2008 06:27, nextgens at freenetproject.org wrote:
> > Author: nextgens
> > Date: 2008-04-04 05:27:02 +0000 (Fri, 04 Apr 2008)
> > New Revision: 18969
> >
> > Modified:
> > trunk/freenet/src/freenet/clients/http/bookmark/BookmarkItem.java
> > Log:
> > implement BookmarkItem.hashCode()
>
> Again, two points:
> - This will change, and therefore break containing HashSet's etc, if the
> parts
> cease to be null. Are they all essential? If they are, are they final, and
> can they be null?
We must do the same checks as for equals()... If it breaks the code somehow we
should fix it.
"This is what the JDK 1.4 API documentation says about the hashCode method of
Object class-
Returns a hash code value for the object. This method is supported for the
benefit of hashtables such as those provided by java.util.Hashtable.
* The general contract of hashCode is: Whenever it is invoked on the same
object more than once during an execution of a Java application, the hashCode
method must consistently return the same integer, provided no information used
in equals comparisons on the object is modified. This integer need not remain
consistent from one execution of an application to another execution of the
same application.
* If two objects are equal according to the equals(Object) method, then
calling the hashCode method on each of the two objects must produce the same
integer result.
* It is not required that if two objects are unequal according to the
equals(java.lang.Object) method, then calling the hashCode method on each of
the two objects must produce distinct integer results. However, the programmer
should be aware that producing distinct integer results for unequal objects may
improve the performance of hashtables.
As much as is reasonably practical, the hashCode method defined by class Object
does return distinct integers for distinct objects. (This is typically
implemented by converting the internal address of the object into an integer,
but this implementation technique is not required by the JavaTM programming
language.) "
http://www.geocities.com/technofundo/tech/java/equalhash.html
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