From Array of Objects to HashMap

[Patrice Ricard]

Hi everyone
I have an Array of Objects of type Result. One of the property of this Object is dictionary.
I want to create a HashMap which keys are the different dictionaries and values are Array of Result that have the same dictionary property.

hope to be clear.

thanks

[Santhosh Kumar]

Sample code could look like,

        Result[] results = getResults();
        Map<String, Result[]> resultsMap = new HashMap<String, Result[]>();
        for (Result result : results) {
            resultsMap.put(result.getDictionary(), result);
        }
    

[Patrice Ricard]

fast reply but that doesn't work
You put a Result Object in the values and not an Array of Result.

[Steve Luke]

Use a MultiHashMap from Apache Commons. Or something similar.

The idea:
1) Map will be Map<Disctionary, List<Results>>.
2) When you get a Dictionary use map.get(dictionary)
3a) If the result is null, make a new List<Results>
3b) Add the current Results object to the List
3c) Put the List back in the Map keyed to the Dictionary

The MultiMap does this for you.

[Santhosh Kumar]

Sorry, should have read the question clearly. Modified code may look like,

        Result[] results = getResults();
        Map<String, List<Result>> resultsMap = new HashMap<String, List<Result>>();
        for (Result result : results) {
            List<Result> resultsList = resultsMap.get(result.getDictionary());
            
            if (resultsList == null) {
                resultsList = new ArrayList<Result>();
                resultsMap.put(result.getDictionary(), resultsList);
            }
            
            resultsList.add(result);
        }
    

And convert the List<Result> to Result[] whenever you want to use the array object. Or if you want to do then itself, loop through the Map, read each list and convert to array object.

As Steve mentioned, MultiHashMap does the same thing.
[ August 19, 2008: Message edited by: Santhosh Kumar ]

[Patrice Ricard]

thanks to both of you and for your quickness.

I was stuck with Array in my mind and didn't think about List.toArray().
[ August 19, 2008: Message edited by: Patrice Ricard ]