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  Returning generic Maps  (Read 426 times)
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Offline Regenuluz
« Posted 2013-04-17 12:45:05 »

Is there a prettier way of doing the following?

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public static <T, E> Map<T, E> loadMap(File file, Map<T, E> map) {
   try {
      FileInputStream fis = new FileInputStream(file);
      ObjectInputStream ois = new ObjectInputStream(fis);
      Object o = ois.readObject();
      if(o instanceof Map) {
         map = (Map<T, E>) o;
         System.out.println(map);
      }

      ois.close();
      fis.close();

      return map;

   } catch(IOException | ClassNotFoundException e) {
      e.printStackTrace();
   }

   return null;
}


At first I didn't return anything, because I thought that Objects(Map in this case) were passed by reference, so I just assigned the value of whatever was read, to passed Map. However, this didn't alter the value outside of the function call.

So now I need a Map to get the types it uses and then return a map. :/

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Map<Foo, Bar> foobar;
foobar = (Map<Foo, Bar>) loadMap(file, foobar);


just isn't as good looking as plain old loadMap(file, foobar); or foobar = loadMap(file) Sad (These two variants is the ones I like the most Tongue (Looks the most pretty xD))

Cheers! Smiley
Offline delt0r

JGO Knight


Medals: 27
Exp: 18 years


Computers can do that?


« Reply #1 - Posted 2013-04-17 13:25:13 »

You could put things into the provided map. As in you don't create a new map object just use the map object that is passed in. Otherwise this is pretty much how it needs to be done due to type erasure.

I have no special talents. I am only passionately curious.--Albert Einstein
Offline Regenuluz
« Reply #2 - Posted 2013-04-17 13:29:42 »

Well, I thought I put the map object into the provided map on line 7, however it only sticks as long as I'm inside the function call, thus I have to return the map.
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Offline delt0r

JGO Knight


Medals: 27
Exp: 18 years


Computers can do that?


« Reply #3 - Posted 2013-04-17 14:20:37 »

Line 7 reassigned  the local variable 'map' to point to a different map object from the one passed in.
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map.putAll((Map<T,E>)o);

Would work.

I have no special talents. I am only passionately curious.--Albert Einstein
Offline Regenuluz
« Reply #4 - Posted 2013-04-17 14:48:42 »

Arh, right. I should've thought of map.putAll(). Smiley

Thanks a bunch!
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