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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 27231] New: - Change to HashEntry inner class of AbstractHashedMap
Date Wed, 25 Feb 2004 17:08:30 GMT
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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=27231

Change to HashEntry inner class of AbstractHashedMap

           Summary: Change to HashEntry inner class of AbstractHashedMap
           Product: Commons
           Version: unspecified
          Platform: All
               URL: http://bblfish.net/java/collections/
        OS/Version: Other
            Status: NEW
          Severity: Enhancement
          Priority: Other
         Component: Collections
        AssignedTo: commons-dev@jakarta.apache.org
        ReportedBy: henry.story@bblfish.net


The way the AbstractHashedMap class is currently written it is not as extensible as it could
be.
The HashEntry static inner class is abstract. By slightly refactoring it to an inner interface
one can get a 
lot more mileage out of it.

This change has minimal impact on four other classes from the map package.

Two extra classes which I will submit as a seperate patch (should I do this before this one
is accepted?)
that use this inner interface are a HashedSet and a WeakHashedSet. Both of these classes are
adapters 
of a subclass of the changed AbstractHashedMap.

The HashEntry interface essentially hides the representation of the key and value objects.
In a HashSet 
the key is the value, so this avoids the duplication - not of objects, but of references.
More importantly 
it also allows a HashEntry to extend a WeakReference Object, which cannot be done as the code

presently stands.

Here is the new interface:

    protected static interface HashEntry  extends Map.Entry, KeyValue {
         public HashEntry getNext();

         public void setNext(HashEntry next);

         public int getHashCode();

         public void setHashCode(int hashCode);

        /**
          * @param key raw key (ie, no interpretation for special cases like NULL
         */

        public void setRawKey(Object key);

        /**
         *
         * @return the raw key
         */
        public Object getRawKey();


    }

This allows the implementation to decide how they can refer to the key and the values. Essentially
we 
remove all reference in the code to the variables 'key' and 'value' and replace them with
the (set/
get)rawkey (set/get)value methods. The raw key method is necessary as the setKey method is
often 
overridden to do special null substition work.

I have also created a more interesting NULL object, that can better describe itself. When
debugging it is 
often helpful to know that one is looking at a NULL object.

Finally I also - and debatably wrongly  - changed the Iterator from  static inner classes
to real inner 
classes. This is how it is meant to work anyway. An inner class just has a reference to its
enclosing 
class. But perhaps there is something here that I have not understood. My other contributions
don't 
hang on this change. They just make the code a little simpler. 
If the intention is to extract these classes to an external package, then the current solution
of having a 
static inner class makes sense.

I will attach class diagrams and diffs to this request to clarify the changes.

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