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  Generics / Design help  (Read 1476 times)
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Offline roland
« Posted 2012-07-22 00:09:41 »

Hey, firstly I don't think this is possible. If it isn't, can anyone recommend a better way of doing it?

I have an abstract class with one field that lots of other classes extend, each having different implementations of some abstract methods:

public abstract class Data
   private DataType dataType;
        public abstract void ...();

DataType is an enum saying what type of data each instance is.

I have a map:

Map<DataType, Set<Data>> allData = new HashMap<DataType, Set<Data>>();

but when i get a value out of the map,

Set<Data> set = allData.get(DataType.X);

I would then have to cast each object inside set to DataX (if that is what the class is called that corresponds with DataType.X)

for (Data d: set)
      DataX dx = (DataX) d; //There is no chance that d won't be of type DataX
      //do something with dx here...

But I know that all the elements inside of set are of type DataX.

Is there any way I can make it so when I get a set out of allData, I can get a set of DataX?

Set<DataX> set = allData.get(DataType.X);

Offline Danny02
« Reply #1 - Posted 2012-07-22 10:21:53 »

when the language is make something really hard for you, you are probably on a wrong way.
Think of another way to story your data or try to explain to us in a wider way what you want to achieve
Offline KnowYourAPI

Junior Newbie

Medals: 1

« Reply #2 - Posted 2012-07-22 10:36:31 »

I don't really know what you want to achieve with this but it looks like you rebuild the whole typing-system.

Instead of making the type of the Data object an instance variable why don't you just create a Class DataX that extends the Data-class? Then you don't have to worry what the type your Data-object is because Java will know the dynamic type of this object and will call the appropriate methods?
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