Re: Wrapping a hashmap put method

[Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>]

Hi Pete,

According to the JavaDocs for java.util.HashMap, the 'put' method is 
supposed to return the object that was previously assigned to the key, 
or else it should return null if no object was previously assigned to 
the key.

I'm looking at these Javadocs:
http://java.sun.com/j2se/1.4.2/docs/api/java/util/HashMap.html

Since you just created the hashmap *immediately* before calling the 
'put' method, I think it's safe to assume that there's nothing assigned 
to any of the keys in the hashmap -- that being the case, 'null' is the 
*expected* return value.

So I guess I don't understand what the issue is?

Your message implies that the Java code doesn't do the same thing -- but 
the Java code that you demonstrated doesn't even attempt to check the 
return value!

Obviously, there's additional code in your application that I haven't 
seen, so maybe I'm missing the point.  Can you show the code that's 
returning a null when it shouldn't be?


Pete Helgren wrote:
> I have been puzzling over how to wrap the HashMap put method.  I 
> successfully (I thought) built prototypes, interfaces and an RPG wrapper 
> to handle the call, but I must be doing something wrong because it is 
> not working. It is returning a null value.
>
> Java Prototypes:
>
> *+++++++++++++++++++++++++++++++
> *  new_jMap
> *      Create a new Java Hashmap object
> *
> *   Returns the new Java HashMap object
> *+++++++++++++++++++++++++++++++
> D new_jMap...
> D                 PR                  like(jMap)
> D                                     ExtProc(*JAVA
> D                                     :'java.util.HashMap'
> D                                     :*CONSTRUCTOR)
> *++++++++++++++++++++++++++++++
> *  jMap_put
> *     Add a key and a value to a hashmap
> *
> *++++++++++++++++++++++++++++++
> D JMAP_put...
> D                 PR                  like(jObject)
> D                                     EXTPROC(*JAVA
> D                                     :'java.util.HashMap'
> D                                     :'put')
> D  key                                like(jObject)
> D  value                              like(jObject)
>
> And the RPG wrapper prototype:
>
> D rre_jMap_put...
> D                 PR                  like(jObject)
> D prMap                               like(jMap)
> D prKey                               like(jObject)
> D prValue                             like(jObject)   
>
> RPG Wrapper program:
> *-------------------------------------------
> * Add elements to a Hashmap
> *
> *-------------------------------------------
> P rre_jMap_put...
> P                 B                   EXPORT
> D rre_jMap_put...
> D                 PI                  like(jObject)
> D    peMap                            like(jMap)
> D    peKey                            like(jobject)
> D    peValue                          like(jObject)
> D
>
>  /free
>
>  peMap = JMAP_put(peMap:peKey:peValue);
>
>  return peMap;
>
> /End-free
> P                 E
>
> Finally when I call it in my program (relevant code):
>
>         lReParam = new_jMap();
>         lkey = new_String('selectName');
>         lvalue = new_String('BALL');
>         lReParam = rre_jMap_put(lReParam:lkey:lvalue);
>
> The thing that I am uncertain about is that when I code in Java, I act 
> on the object directly rather than passing it back and forth (it may be 
> a shorthand way, I don't know).  So in Java I would do this:
>
>  HashMap reportParameters = new HashMap();
>  reportParameters.put("selectName", "BALL");
>
> But even changing the RPG code above to this:
>
>  lReParam = new_jMap();
>  lkey = new_String('selectName');
>  lvalue = new_String('BALL');
>  rre_jMap_put(lReParam:lkey:lvalue);
>
> Has the same result which is a null value for the key/value pair.
>
> I am missing something.  Any suggestions? 
>
> Thanks,
>
> Pete